From 3b9b4ea06f62ec891e1a3e2be7badb998efed204 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 14 May 2017 20:57:08 +0100
Subject: [PATCH 01/20] Small fix for auto-indexing

---
 holoviews/core/data/array.py      | 11 ++++++-----
 holoviews/core/data/dictionary.py |  2 +-
 holoviews/core/data/pandas.py     |  4 ++--
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/holoviews/core/data/array.py b/holoviews/core/data/array.py
index 69a55c2864..722abe399f 100644
--- a/holoviews/core/data/array.py
+++ b/holoviews/core/data/array.py
@@ -54,18 +54,19 @@ def init(cls, eltype, data, kdims, vdims):
             except:
                 data = None
 
+        if kdims is None:
+            kdims = eltype.kdims
+        if vdims is None:
+            vdims = eltype.vdims
+
         if data is None or data.ndim > 2 or data.dtype.kind in ['S', 'U', 'O']:
             raise ValueError("ArrayInterface interface could not handle input type.")
         elif data.ndim == 1:
-            if eltype._auto_indexable_1d:
+            if eltype._auto_indexable_1d and len(kdims)+len(vdims)>1:
                 data = np.column_stack([np.arange(len(data)), data])
             else:
                 data = np.atleast_2d(data).T
 
-        if kdims is None:
-            kdims = eltype.kdims
-        if vdims is None:
-            vdims = eltype.vdims
         return data, {'kdims':kdims, 'vdims':vdims}, {}
 
     @classmethod
diff --git a/holoviews/core/data/dictionary.py b/holoviews/core/data/dictionary.py
index 7668f54898..812e88cc6b 100644
--- a/holoviews/core/data/dictionary.py
+++ b/holoviews/core/data/dictionary.py
@@ -49,7 +49,7 @@ def init(cls, eltype, data, kdims, vdims):
             data = {d: data[d] for d in dimensions}
         elif isinstance(data, np.ndarray):
             if data.ndim == 1:
-                if eltype._auto_indexable_1d:
+                if eltype._auto_indexable_1d and len(kdims)+len(vdims)>1:
                     data = np.column_stack([np.arange(len(data)), data])
                 else:
                     data = np.atleast_2d(data).T
diff --git a/holoviews/core/data/pandas.py b/holoviews/core/data/pandas.py
index cee7e6e2fe..0e9e0e96d8 100644
--- a/holoviews/core/data/pandas.py
+++ b/holoviews/core/data/pandas.py
@@ -61,8 +61,8 @@ def init(cls, eltype, data, kdims, vdims):
                 data = cyODict(((c, col) for c, col in zip(columns, column_data)))
             elif isinstance(data, np.ndarray):
                 if data.ndim == 1:
-                    if eltype._auto_indexable_1d:
-                        data = (range(len(data)), data)
+                    if eltype._auto_indexable_1d and len(kdims)+len(vdims)>1:
+                        data = (np.arange(len(data)), data)
                     else:
                         data = np.atleast_2d(data).T
                 else:

From c2bc41be3a1801dd44ca06df8a6e3a66a1f63bf4 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 14 May 2017 20:59:18 +0100
Subject: [PATCH 02/20] Added iloc tabular indexing interface

---
 holoviews/core/data/__init__.py   |  10 +-
 holoviews/core/data/array.py      |  19 +++
 holoviews/core/data/dask.py       |  26 +++-
 holoviews/core/data/dictionary.py |  25 ++++
 holoviews/core/data/grid.py       |  23 ++++
 holoviews/core/data/interface.py  |  47 ++++++++
 holoviews/core/data/ndelement.py  |  27 ++++-
 holoviews/core/data/pandas.py     |  21 ++++
 tests/testdataset.py              | 194 ++++++++++++++++++++++++++++--
 9 files changed, 380 insertions(+), 12 deletions(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index b7baec5abe..90dd463a6e 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -9,7 +9,7 @@
 import param
 
 from ..dimension import redim
-from .interface import Interface
+from .interface import Interface, TabularIndex
 from .array import ArrayInterface
 from .dictionary import DictInterface
 from .grid import GridInterface
@@ -624,6 +624,14 @@ def to(self):
         return self._conversion_interface(self)
 
 
+    @property
+    def iloc(self):
+        """
+        Returns a TabularIndex, providing a convenient interface to
+        slice and index into the Dataset using row and column indices.
+        """
+        return TabularIndex(self)
+
 
 # Aliases for pickle backward compatibility
 Columns      = Dataset
diff --git a/holoviews/core/data/array.py b/holoviews/core/data/array.py
index 722abe399f..073258a246 100644
--- a/holoviews/core/data/array.py
+++ b/holoviews/core/data/array.py
@@ -233,4 +233,23 @@ def aggregate(cls, dataset, dimensions, function, **kwargs):
         return np.atleast_2d(rows)
 
 
+    @classmethod
+    def iloc(cls, dataset, index):
+        rows, cols = index
+        if np.isscalar(cols):
+            if isinstance(cols, util.basestring):
+                cols = dataset.get_dimension_index(cols)
+            if np.isscalar(rows):
+                return dataset.data[rows, cols]
+            cols = [dataset.get_dimension_index(cols)]
+        elif not isinstance(cols, slice):
+            cols = [dataset.get_dimension_index(d) for d in cols]
+
+        if np.isscalar(rows):
+            rows = [rows]
+        data = dataset.data[rows, :][:, cols]
+        if data.ndim == 1:
+            return np.atleast_2d(data).T
+        return data
+
 Interface.register(ArrayInterface)
diff --git a/holoviews/core/data/dask.py b/holoviews/core/data/dask.py
index 88e4ca21a9..984dbd8efc 100644
--- a/holoviews/core/data/dask.py
+++ b/holoviews/core/data/dask.py
@@ -12,7 +12,7 @@
 
 from .. import util
 from ..element import Element
-from ..ndmapping import NdMapping, item_check
+from ..ndmapping import NdMapping, item_check, OrderedDict
 from .interface import Interface
 from .pandas import PandasInterface
 
@@ -241,6 +241,30 @@ def dframe(cls, columns, dimensions):
     def nonzero(cls, dataset):
         return True
 
+    @classmethod
+    def iloc(cls, dataset, index):
+        """
+        Dask does not support iloc, therefore iloc will execute
+        the call graph and lose the laziness of the operation.
+        """
+        rows, cols = index
+        scalar = False
+        if isinstance(cols, slice):
+            cols = [d.name for d in dataset.dimensions()][cols]
+        elif np.isscalar(cols):
+            scalar = np.isscalar(rows)
+            cols = [dataset.get_dimension(cols).name]
+        else:
+            cols = [dataset.get_dimension(d).name for d in index[1]]
+        if np.isscalar(rows):
+            rows = [rows]
+
+        data = OrderedDict()
+        for c in cols:
+            data[c] = dataset.data[c].compute().iloc[rows].values
+        if scalar:
+            return data[cols[0]][0]
+        return tuple(data.values())
 
 
 Interface.register(DaskInterface)
diff --git a/holoviews/core/data/dictionary.py b/holoviews/core/data/dictionary.py
index 812e88cc6b..e912aa3a9b 100644
--- a/holoviews/core/data/dictionary.py
+++ b/holoviews/core/data/dictionary.py
@@ -261,4 +261,29 @@ def aggregate(cls, dataset, kdims, function, **kwargs):
         return aggregated
 
 
+    @classmethod
+    def iloc(cls, dataset, index):
+        rows, cols = index
+        scalar = False
+        if np.isscalar(cols):
+            scalar = np.isscalar(rows)
+            cols = [dataset.get_dimension(cols, strict=True)]
+        elif isinstance(cols, slice):
+            cols = dataset.dimensions()[cols]
+        else:
+            cols = [dataset.get_dimension(d, strict=True) for d in cols]
+
+        if np.isscalar(rows):
+            rows = [rows]
+
+        new_data = OrderedDict()
+        for d, values in dataset.data.items():
+            if d in cols:
+                new_data[d] = values[rows]
+
+        if scalar:
+            return new_data[cols[0].name][0]
+        return new_data
+
+
 Interface.register(DictInterface)
diff --git a/holoviews/core/data/grid.py b/holoviews/core/data/grid.py
index 45fecb8d5b..1c42d511c0 100644
--- a/holoviews/core/data/grid.py
+++ b/holoviews/core/data/grid.py
@@ -391,5 +391,28 @@ def sort(cls, dataset, by=[]):
             raise Exception('Compressed format cannot be sorted, either instantiate '
                             'in the desired order or use the expanded format.')
 
+    @classmethod
+    def iloc(cls, dataset, index):
+        rows, cols = index
+        scalar = False
+        if np.isscalar(cols):
+            scalar = np.isscalar(rows)
+            cols = [dataset.get_dimension(cols, strict=True)]
+        elif isinstance(cols, slice):
+            cols = dataset.dimensions()[cols]
+        else:
+            cols = [dataset.get_dimension(d, strict=True) for d in cols]
+
+        if np.isscalar(rows):
+            rows = [rows]
+
+        new_data = []
+        for d in cols:
+            new_data.append(dataset.dimension_values(d)[rows])
+
+        if scalar:
+            return new_data[0][0]
+        return tuple(new_data)
+
 
 Interface.register(GridInterface)
diff --git a/holoviews/core/data/interface.py b/holoviews/core/data/interface.py
index 6b7d528da3..f25fbea38a 100644
--- a/holoviews/core/data/interface.py
+++ b/holoviews/core/data/interface.py
@@ -6,6 +6,53 @@
 from .. import util
 
 
+class TabularIndex(object):
+    """
+    TabularIndex is small wrapper object that allows row, column
+    based indexing into a Dataset using the ``iloc`` property.
+    It supports the usual numpy and pandas iloc indexing semantics
+    including integer indices, slices, lists and arrays of values.
+    """
+
+    def __init__(self, dataset):
+        self.dataset = dataset
+
+    def __getitem__(self, index):
+        index = util.wrap_tuple(index)
+        if len(index) == 1:
+            index = (index[0], slice(None))
+        elif len(index) > 2:
+            raise IndexError('Tabular index not understood, index '
+                             'must be at most length 2.')
+
+        rows, cols = index
+        if rows is Ellipsis:
+            rows = slice(None)
+        data = self.dataset.interface.iloc(self.dataset, (rows, cols))
+        kdims = self.dataset.kdims
+        vdims = self.dataset.vdims
+        if np.isscalar(data):
+            return data
+        elif cols == slice(None):
+            pass
+        else:
+            if isinstance(cols, slice):
+                dims = self.dataset.dimensions()[index[1]]
+            elif np.isscalar(cols):
+                dims = [self.dataset.get_dimension(cols)]
+            else:
+                dims = [self.dataset.get_dimension(d) for d in cols]
+            kdims = [d for d in dims if d in kdims]
+            vdims = [d for d in dims if d in vdims]
+
+        datatype = [dt for dt in self.dataset.datatype
+                    if dt in Interface.interfaces and
+                    not Interface.interfaces[dt].gridded]
+        if not datatype: datatype = ['dataframe', 'dictionary']
+        return self.dataset.clone(data, kdims=kdims, vdims=vdims,
+                                  datatype=datatype)
+
+
 class Interface(param.Parameterized):
 
     interfaces = {}
diff --git a/holoviews/core/data/ndelement.py b/holoviews/core/data/ndelement.py
index 066b0dba34..dcc6e03bf4 100644
--- a/holoviews/core/data/ndelement.py
+++ b/holoviews/core/data/ndelement.py
@@ -8,7 +8,7 @@
 from .interface import Interface
 from ..dimension import Dimension, Dimensioned
 from ..element import NdElement
-from ..ndmapping import item_check
+from ..ndmapping import item_check, OrderedDict
 from .. import util
 
 
@@ -141,5 +141,30 @@ def unpack_scalar(cls, columns, data):
         else:
             return data
 
+    @classmethod
+    def iloc(cls, dataset, index):
+        data = dataset.columns()
+        rows, cols = index
+        scalar = False
+        if np.isscalar(cols):
+            scalar = np.isscalar(rows)
+            cols = [dataset.get_dimension(cols, strict=True)]
+        elif isinstance(cols, slice):
+            cols = dataset.dimensions()[cols]
+        else:
+            cols = [dataset.get_dimension(d, strict=True) for d in cols]
+
+        if np.isscalar(rows):
+            rows = [rows]
+
+        new_data = OrderedDict()
+        for d, values in data.items():
+            if d in cols:
+                new_data[d] = values[rows]
+
+        if scalar:
+            return new_data[cols[0].name][0]
+        return new_data
+
 
 Interface.register(NdElementInterface)
diff --git a/holoviews/core/data/pandas.py b/holoviews/core/data/pandas.py
index 0e9e0e96d8..c49d6ac01a 100644
--- a/holoviews/core/data/pandas.py
+++ b/holoviews/core/data/pandas.py
@@ -252,4 +252,25 @@ def dframe(cls, columns, dimensions):
             return columns.data.copy()
 
 
+    @classmethod
+    def iloc(cls, dataset, index):
+        rows, cols = index
+        scalar = False
+        columns = list(dataset.data.columns)
+        if isinstance(cols, slice):
+            cols = [d.name for d in dataset.dimensions()][cols]
+        elif np.isscalar(cols):
+            scalar = np.isscalar(rows)
+            cols = [dataset.get_dimension(cols).name]
+        else:
+            cols = [dataset.get_dimension(d).name for d in index[1]]
+        cols = [columns.index(c) for c in cols]
+        if np.isscalar(rows):
+            rows = [rows]
+
+        if scalar:
+            return dataset.data.iloc[rows[0], cols[0]]
+        return dataset.data.iloc[rows, cols]
+
+
 Interface.register(PandasInterface)
diff --git a/tests/testdataset.py b/tests/testdataset.py
index 87bb4ee86b..99835b14eb 100644
--- a/tests/testdataset.py
+++ b/tests/testdataset.py
@@ -59,10 +59,10 @@ def setUp(self):
         self.data_instance_type = None
 
     def init_column_data(self):
-        self.xs = range(11)
-        self.xs_2 = [el**2 for el in self.xs]
+        self.xs = np.array(range(11))
+        self.xs_2 = self.xs**2
 
-        self.y_ints = [i*2 for i in range(11)]
+        self.y_ints = self.xs*2
         self.dataset_hm = Dataset((self.xs, self.y_ints),
                                   kdims=['x'], vdims=['y'])
         self.dataset_hm_alias = Dataset((self.xs, self.y_ints),
@@ -248,6 +248,89 @@ def test_dataset_array_ht(self):
         self.assertEqual(self.dataset_hm.array(),
                          np.column_stack([self.xs, self.y_ints]))
 
+    # Tabular indexing
+
+    def test_dataset_iloc_slice_rows(self):
+        sliced = self.dataset_hm.iloc[1:4]
+        table = Dataset({'x': self.xs[1:4], 'y': self.y_ints[1:4]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_slice_rows_slice_cols(self):
+        sliced = self.dataset_hm.iloc[1:4, 1:]
+        table = Dataset({'y': self.y_ints[1:4]}, kdims=[], vdims=['y'],
+                        datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_slice_rows_list_cols(self):
+        sliced = self.dataset_hm.iloc[1:4, [0, 1]]
+        table = Dataset({'x': self.xs[1:4], 'y': self.y_ints[1:4]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_slice_rows_index_cols(self):
+        sliced = self.dataset_hm.iloc[1:4, 1]
+        table = Dataset({'y': self.y_ints[1:4]}, kdims=[], vdims=['y'],
+                        datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows(self):
+        sliced = self.dataset_hm.iloc[[0, 2]]
+        table = Dataset({'x': self.xs[[0, 2]], 'y': self.y_ints[[0, 2]]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows_list_cols(self):
+        sliced = self.dataset_hm.iloc[[0, 2], [0, 1]]
+        table = Dataset({'x': self.xs[[0, 2]], 'y': self.y_ints[[0, 2]]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows_list_cols_by_name(self):
+        sliced = self.dataset_hm.iloc[[0, 2], ['x', 'y']]
+        table = Dataset({'x': self.xs[[0, 2]], 'y': self.y_ints[[0, 2]]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows_slice_cols(self):
+        sliced = self.dataset_hm.iloc[[0, 2], slice(0, 2)]
+        table = Dataset({'x': self.xs[[0, 2]], 'y': self.y_ints[[0, 2]]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_index_rows_index_cols(self):
+        indexed = self.dataset_hm.iloc[1, 1]
+        self.assertEqual(indexed, self.y_ints[1])
+
+    def test_dataset_iloc_index_rows_slice_cols(self):
+        indexed = self.dataset_hm.iloc[1, :2]
+        table = Dataset({'x':self.xs[[1]],  'y':self.y_ints[[1]]},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(indexed, table)
+
+    def test_dataset_iloc_list_cols(self):
+        sliced = self.dataset_hm.iloc[:, [0, 1]]
+        table = Dataset({'x':self.xs,  'y':self.y_ints},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_cols_by_name(self):
+        sliced = self.dataset_hm.iloc[:, ['x', 'y']]
+        table = Dataset({'x':self.xs,  'y':self.y_ints},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_ellipsis_list_cols(self):
+        sliced = self.dataset_hm.iloc[..., [0, 1]]
+        table = Dataset({'x':self.xs,  'y':self.y_ints},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_ellipsis_list_cols_by_name(self):
+        sliced = self.dataset_hm.iloc[..., ['x', 'y']]
+        table = Dataset({'x':self.xs,  'y':self.y_ints},
+                        kdims=['x'], vdims=['y'], datatype=['dictionary'])
+        self.assertEqual(sliced, table)
 
 
 class HeterogeneousColumnTypes(HomogeneousColumnTypes):
@@ -258,8 +341,8 @@ class HeterogeneousColumnTypes(HomogeneousColumnTypes):
     def init_column_data(self):
         self.kdims = ['Gender', 'Age']
         self.vdims = ['Weight', 'Height']
-        self.gender, self.age = ['M','M','F'], [10,16,12]
-        self.weight, self.height = [15,18,10], [0.8,0.6,0.8]
+        self.gender, self.age = np.array(['M','M','F']), np.array([10,16,12])
+        self.weight, self.height = np.array([15,18,10]), np.array([0.8,0.6,0.8])
         self.table = Dataset({'Gender':self.gender, 'Age':self.age,
                               'Weight':self.weight, 'Height':self.height},
                              kdims=self.kdims, vdims=self.vdims)
@@ -551,6 +634,91 @@ def test_dataset_value_dim_scalar_index(self):
         row = self.table['M', 10, 'Weight']
         self.assertEquals(row, 15)
 
+    # Tabular indexing
+
+    def test_dataset_iloc_slice_rows(self):
+        sliced = self.table.iloc[1:2]
+        table = Dataset({'Gender':self.gender[1:2], 'Age':self.age[1:2],
+                         'Weight':self.weight[1:2], 'Height':self.height[1:2]},
+                        kdims=self.kdims, vdims=self.vdims)
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_slice_rows_slice_cols(self):
+        sliced = self.table.iloc[1:2, 1:3]
+        table = Dataset({'Age':self.age[1:2], 'Weight':self.weight[1:2]},
+                        kdims=self.kdims[1:], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_slice_rows_list_cols(self):
+        sliced = self.table.iloc[1:2, [1, 3]]
+        table = Dataset({'Age':self.age[1:2], 'Height':self.height[1:2]},
+                        kdims=self.kdims[1:], vdims=self.vdims[1:])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_slice_rows_index_cols(self):
+        sliced = self.table.iloc[1:2, 2]
+        table = Dataset({'Weight':self.weight[1:2]}, kdims=[], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows(self):
+        sliced = self.table.iloc[[0, 2]]
+        table = Dataset({'Gender':self.gender[[0, 2]], 'Age':self.age[[0, 2]],
+                         'Weight':self.weight[[0, 2]], 'Height':self.height[[0, 2]]},
+                        kdims=self.kdims, vdims=self.vdims)
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows_list_cols(self):
+        sliced = self.table.iloc[[0, 2], [0, 2]]
+        table = Dataset({'Gender':self.gender[[0, 2]],  'Weight':self.weight[[0, 2]]},
+                        kdims=self.kdims[:1], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows_list_cols_by_name(self):
+        sliced = self.table.iloc[[0, 2], ['Gender', 'Weight']]
+        table = Dataset({'Gender':self.gender[[0, 2]],  'Weight':self.weight[[0, 2]]},
+                        kdims=self.kdims[:1], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_rows_slice_cols(self):
+        sliced = self.table.iloc[[0, 2], slice(1, 3)]
+        table = Dataset({'Age':self.age[[0, 2]],  'Weight':self.weight[[0, 2]]},
+                        kdims=self.kdims[1:], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_index_rows_index_cols(self):
+        indexed = self.table.iloc[1, 1]
+        self.assertEqual(indexed, self.age[1])
+
+    def test_dataset_iloc_index_rows_slice_cols(self):
+        indexed = self.table.iloc[1, 1:3]
+        table = Dataset({'Age':self.age[[1]],  'Weight':self.weight[[1]]},
+                        kdims=self.kdims[1:], vdims=self.vdims[:1])
+        self.assertEqual(indexed, table)
+
+    def test_dataset_iloc_list_cols(self):
+        sliced = self.table.iloc[:, [0, 2]]
+        table = Dataset({'Gender':self.gender,  'Weight':self.weight},
+                        kdims=self.kdims[:1], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_list_cols_by_name(self):
+        sliced = self.table.iloc[:, ['Gender', 'Weight']]
+        table = Dataset({'Gender':self.gender,  'Weight':self.weight},
+                        kdims=self.kdims[:1], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_ellipsis_list_cols(self):
+        sliced = self.table.iloc[..., [0, 2]]
+        table = Dataset({'Gender':self.gender,  'Weight':self.weight},
+                        kdims=self.kdims[:1], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
+    def test_dataset_iloc_ellipsis_list_cols_by_name(self):
+        sliced = self.table.iloc[..., ['Gender', 'Weight']]
+        table = Dataset({'Gender':self.gender,  'Weight':self.weight},
+                        kdims=self.kdims[:1], vdims=self.vdims[:1])
+        self.assertEqual(sliced, table)
+
     # Casting
 
     def test_dataset_array_ht(self):
@@ -562,6 +730,9 @@ class ArrayDatasetTest(HomogeneousColumnTypes, ComparisonTestCase):
     """
     Test of the ArrayDataset interface.
     """
+
+    datatype = 'array'
+
     def setUp(self):
         self.restore_datatype = Dataset.datatype
         Dataset.datatype = ['array']
@@ -574,6 +745,8 @@ class DFDatasetTest(HeterogeneousColumnTypes, ComparisonTestCase):
     Test of the pandas DFDataset interface.
     """
 
+    datatype = 'dataframe'
+
     def setUp(self):
         if pd is None:
             raise SkipTest("Pandas not available")
@@ -588,6 +761,8 @@ class DaskDatasetTest(HeterogeneousColumnTypes, ComparisonTestCase):
     Test of the pandas DaskDataset interface.
     """
 
+    datatype = 'dask'
+
     def setUp(self):
         if dd is None:
             raise SkipTest("dask not available")
@@ -630,6 +805,8 @@ class DictDatasetTest(HeterogeneousColumnTypes, ComparisonTestCase):
     Test of the generic dictionary interface.
     """
 
+    datatype = 'dictionary'
+
     def setUp(self):
         self.restore_datatype = Dataset.datatype
         Dataset.datatype = ['dictionary']
@@ -698,10 +875,9 @@ def setUp(self):
         self.init_data()
 
     def init_column_data(self):
-        self.xs = range(11)
-        self.xs_2 = [el**2 for el in self.xs]
-
-        self.y_ints = [i*2 for i in range(11)]
+        self.xs = np.arange(11)
+        self.xs_2 = self.xs**2
+        self.y_ints = self.xs*2
         self.dataset_hm = Dataset((self.xs, self.y_ints),
                                   kdims=['x'], vdims=['y'])
         self.dataset_hm_alias = Dataset((self.xs, self.y_ints),

From 48d7a06ce6eef17b85eae95777f42bbf83d3fb8e Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 12:21:31 +0100
Subject: [PATCH 03/20] Small docstring improvements

---
 holoviews/core/data/__init__.py  | 4 +++-
 holoviews/core/data/interface.py | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index 90dd463a6e..f82c2e9a64 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -628,7 +628,9 @@ def to(self):
     def iloc(self):
         """
         Returns a TabularIndex, providing a convenient interface to
-        slice and index into the Dataset using row and column indices.
+        slice and index into the Dataset using row and column indices,
+        allow selection by integer index, slice and list of integer
+        indices and boolean arrays.
         """
         return TabularIndex(self)
 
diff --git a/holoviews/core/data/interface.py b/holoviews/core/data/interface.py
index f25fbea38a..9a0d888a6c 100644
--- a/holoviews/core/data/interface.py
+++ b/holoviews/core/data/interface.py
@@ -9,7 +9,7 @@
 class TabularIndex(object):
     """
     TabularIndex is small wrapper object that allows row, column
-    based indexing into a Dataset using the ``iloc`` property.
+    based indexing into a Dataset using the ``.iloc`` property.
     It supports the usual numpy and pandas iloc indexing semantics
     including integer indices, slices, lists and arrays of values.
     """

From ddff78553cac14c897ca5edcdb62b58a3c5f13ae Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 12:25:20 +0100
Subject: [PATCH 04/20] Updated Point selection example to use .iloc

---
 examples/streams/bokeh/point_selection1D.ipynb | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/examples/streams/bokeh/point_selection1D.ipynb b/examples/streams/bokeh/point_selection1D.ipynb
index 33f092775f..1e1b84e332 100644
--- a/examples/streams/bokeh/point_selection1D.ipynb
+++ b/examples/streams/bokeh/point_selection1D.ipynb
@@ -42,12 +42,12 @@
     "\n",
     "# Write function that uses the selection indices to slice points and compute stats\n",
     "def selected_info(index):\n",
-    "    arr = points.array()[index]\n",
+    "    selected = points.iloc[index]\n",
     "    if index:\n",
-    "        label = 'Mean x, y: %.3f, %.3f' % tuple(arr.mean(axis=0))\n",
+    "        label = 'Mean x, y: %.3f, %.3f' % tuple(selected.array().mean(axis=0))\n",
     "    else:\n",
     "        label = 'No selection'\n",
-    "    return points.clone(arr, label=label)(style=dict(color='red'))\n",
+    "    return selected.relabel(label)(style=dict(color='red'))\n",
     "\n",
     "# Combine points and DynamicMap\n",
     "points + hv.DynamicMap(selected_info, streams=[selection])"

From 0fcf16156b234cac40227a4f9d454a3b9121d2e6 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 12:32:02 +0100
Subject: [PATCH 05/20] Renamed TabularIndex object to iloc

---
 holoviews/core/data/__init__.py  |  6 +++---
 holoviews/core/data/interface.py | 10 +++++-----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index f82c2e9a64..3f1a1bb718 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -9,7 +9,7 @@
 import param
 
 from ..dimension import redim
-from .interface import Interface, TabularIndex
+from .interface import Interface, iloc
 from .array import ArrayInterface
 from .dictionary import DictInterface
 from .grid import GridInterface
@@ -627,12 +627,12 @@ def to(self):
     @property
     def iloc(self):
         """
-        Returns a TabularIndex, providing a convenient interface to
+        Returns an iloc object, providing a convenient interface to
         slice and index into the Dataset using row and column indices,
         allow selection by integer index, slice and list of integer
         indices and boolean arrays.
         """
-        return TabularIndex(self)
+        return iloc(self)
 
 
 # Aliases for pickle backward compatibility
diff --git a/holoviews/core/data/interface.py b/holoviews/core/data/interface.py
index 9a0d888a6c..645d96d48d 100644
--- a/holoviews/core/data/interface.py
+++ b/holoviews/core/data/interface.py
@@ -6,12 +6,12 @@
 from .. import util
 
 
-class TabularIndex(object):
+class iloc(object):
     """
-    TabularIndex is small wrapper object that allows row, column
-    based indexing into a Dataset using the ``.iloc`` property.
-    It supports the usual numpy and pandas iloc indexing semantics
-    including integer indices, slices, lists and arrays of values.
+    iloc is small wrapper object that allows row, column based
+    indexing into a Dataset using the ``.iloc`` property.  It supports
+    the usual numpy and pandas iloc indexing semantics including
+    integer indices, slices, lists and arrays of values.
     """
 
     def __init__(self, dataset):

From c93995c9767aee262090745c3a4e034c1d168e35 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 14:27:04 +0100
Subject: [PATCH 06/20] Added ndloc indexing interface

---
 holoviews/core/data/__init__.py  |  7 ++++-
 holoviews/core/data/grid.py      | 49 +++++++++++++++++++++++++++++++-
 holoviews/core/data/image.py     |  7 +++++
 holoviews/core/data/interface.py | 21 ++++++++++++++
 4 files changed, 82 insertions(+), 2 deletions(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index 3f1a1bb718..f5be2c39bc 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -9,7 +9,7 @@
 import param
 
 from ..dimension import redim
-from .interface import Interface, iloc
+from .interface import Interface, iloc, ndloc
 from .array import ArrayInterface
 from .dictionary import DictInterface
 from .grid import GridInterface
@@ -635,6 +635,11 @@ def iloc(self):
         return iloc(self)
 
 
+    @property
+    def ndloc(self):
+        return ndloc(self)
+
+
 # Aliases for pickle backward compatibility
 Columns      = Dataset
 ArrayColumns = ArrayInterface
diff --git a/holoviews/core/data/grid.py b/holoviews/core/data/grid.py
index 1c42d511c0..a66949aaa8 100644
--- a/holoviews/core/data/grid.py
+++ b/holoviews/core/data/grid.py
@@ -1,4 +1,4 @@
-from collections import OrderedDict, defaultdict
+from collections import OrderedDict, defaultdict, Iterable
 
 try:
     import itertools.izip as zip
@@ -167,6 +167,53 @@ def canonicalize(cls, dataset, data, coord_dims=None):
         return data
 
 
+    @classmethod
+    def invert_index(cls, index, length):
+        if np.isscalar(index):
+            return length - index
+        elif isinstance(index, slice):
+            start, stop = index.start, index.stop
+            new_start, new_stop = None, None
+            if start is not None:
+                new_stop = length - start
+            if stop is not None:
+                new_start = length - stop
+            return slice(new_start-1, new_stop-1)
+        elif isinstance(index, Iterable):
+            new_index = []
+            for ind in index:
+                new_index.append(length-ind)
+        return new_index
+
+
+    @classmethod
+    def ndloc(cls, dataset, indices):
+        selected = {}
+        adjusted_inds = []
+        all_scalar = True
+        for kd, ind in zip(dataset.kdims[::-1], indices):
+            coords = cls.coords(dataset, kd.name)
+            if np.all(coords[1:] < coords[:-1]):
+                ind = cls.invert_index(ind, len(coords))
+            if np.isscalar(ind):
+                ind = [ind]
+            else:
+                all_scalar = False
+            selected[kd.name] = coords[ind]
+            adjusted_inds.append(ind)
+        for kd in dataset.kdims:
+            if kd.name not in selected:
+                coords = cls.coords(dataset, kd.name)
+                selected[kd.name] = coords
+                all_scalar = False
+        for vd in dataset.vdims:
+            arr = dataset.dimension_values(vd, flat=False)
+            if all_scalar and len(dataset.vdims) == 1:
+                return arr[tuple(ind[0] for ind in adjusted_inds)]
+            selected[vd.name] = arr[tuple(adjusted_inds)]
+        return tuple(selected[d.name] for d in dataset.dimensions())
+
+
     @classmethod
     def values(cls, dataset, dim, expanded=True, flat=True):
         dim = dataset.get_dimension(dim, strict=True)
diff --git a/holoviews/core/data/image.py b/holoviews/core/data/image.py
index 81a8bbb837..70ac560ffd 100644
--- a/holoviews/core/data/image.py
+++ b/holoviews/core/data/image.py
@@ -89,6 +89,13 @@ def reindex(cls, dataset, kdims=None, vdims=None):
             return data[..., inds] if len(inds) > 1 else data[..., inds[0]]
         return data
 
+    @classmethod
+    def coords(cls, dataset, dim, ordered=False, expanded=False):
+        dim = dataset.get_dimension(dim, strict=True)
+        if expanded:
+            return util.expand_grid_coords(dataset, dim)
+        return cls.values(dataset, dim, expanded=False)
+
     @classmethod
     def range(cls, obj, dim):
         dim_idx = obj.get_dimension_index(dim)
diff --git a/holoviews/core/data/interface.py b/holoviews/core/data/interface.py
index 645d96d48d..6c0a49ae14 100644
--- a/holoviews/core/data/interface.py
+++ b/holoviews/core/data/interface.py
@@ -53,6 +53,27 @@ def __getitem__(self, index):
                                   datatype=datatype)
 
 
+class ndloc(object):
+
+    def __init__(self, dataset):
+        self.dataset = dataset
+
+    def __getitem__(self, indices):
+        ds = self.dataset
+        indices = util.wrap_tuple(indices)
+        if not ds.interface.gridded:
+            raise IndexError('Cannot use ndloc on non nd-dimensional datastructure')
+        selected = self.dataset.interface.ndloc(ds, indices)
+        if np.isscalar(selected):
+            return selected
+        datatype = [dt for dt in ds.datatype if dt in Interface.interfaces and
+                    Interface.interfaces[dt].gridded]
+        params = {}
+        if hasattr(ds, 'bounds'):
+            params['bounds'] = None
+        return self.dataset.clone(selected, datatype=[ds.interface.datatype]+datatype, **params)
+
+
 class Interface(param.Parameterized):
 
     interfaces = {}

From 0d2a9c14c4632905b6bd05027dcfb2d0badf49c0 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 16:48:09 +0100
Subject: [PATCH 07/20] Implemented Image indexing using ndloc

---
 holoviews/core/util.py      |  2 +-
 holoviews/element/raster.py | 28 ++++++++++++++++++----------
 tests/testdataset.py        |  6 +++---
 3 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/holoviews/core/util.py b/holoviews/core/util.py
index e8770dd233..b93f89e1da 100644
--- a/holoviews/core/util.py
+++ b/holoviews/core/util.py
@@ -1449,7 +1449,7 @@ def bound_range(vals, density):
     """
     low, high = vals.min(), vals.max()
     invert = False
-    if vals[0] > vals[1]:
+    if len(vals) > 1 and vals[0] > vals[1]:
         invert = True
     if not density:
         density = round(1./((high-low)/(len(vals)-1)), sys.float_info.dig)
diff --git a/holoviews/element/raster.py b/holoviews/element/raster.py
index d629a3fc57..d4c3e58fab 100644
--- a/holoviews/element/raster.py
+++ b/holoviews/element/raster.py
@@ -7,7 +7,7 @@
 from ..core.data import ImageInterface
 from ..core import Dimension, Element2D, Overlay, Dataset
 from ..core.boundingregion import BoundingRegion, BoundingBox
-from ..core.sheetcoords import SheetCoordinateSystem
+from ..core.sheetcoords import SheetCoordinateSystem, Slice
 from ..core.util import max_range
 from .chart import Curve
 from .tabular import Table
@@ -298,21 +298,29 @@ def select(self, selection_specs=None, **selection):
         coords = tuple(selection[kd.name] if kd.name in selection else slice(None)
                        for kd in self.kdims)
 
+        shape = self.interface.shape(self, gridded=True)
         if any([isinstance(el, slice) for el in coords]):
-            shape = self.interface.shape(self, gridded=True)
             bounds = compute_slice_bounds(coords, self, shape[:2])
 
             xdim, ydim = self.kdims
             l, b, r, t = bounds.lbrt()
-            selection = {xdim.name: slice(l, r), ydim.name: slice(b, t)}
-        else:
-            selection = {kd.name: c for kd, c in zip(self.kdims, self.closest(coords))}
 
-        data = self.interface.select(self, **selection)
-        if isinstance(data, np.ndarray) and data.ndim == 1:
-            return self.clone([tuple(data)], kdims=[], new_type=Dataset)
-        elif np.isscalar(data):
-            return data
+            # Situate resampled region into overall slice
+            y0, y1, x0, x1 = Slice(bounds, self)
+            y0, y1 = shape[0]-y1, shape[0]-y0
+            selection = (slice(y0, y1), slice(x0, x1))
+            sliced = True
+        else:
+            y, x = self.sheet2matrixidx(coords[0], coords[1])
+            y = shape[0]-y-1
+            selection = (y, x)
+            sliced = False
+
+        data = self.interface.ndloc(self, selection)
+        if not sliced:
+            if np.isscalar(data):
+                return data
+            return self.clone(data[self.ndims:], kdims=[], new_type=Dataset)
         else:
             return self.clone(data, xdensity=self.xdensity,
                               ydensity=self.ydensity, bounds=bounds)
diff --git a/tests/testdataset.py b/tests/testdataset.py
index 99835b14eb..4d7d10345b 100644
--- a/tests/testdataset.py
+++ b/tests/testdataset.py
@@ -884,9 +884,9 @@ def init_column_data(self):
                                         kdims=[('x', 'X')], vdims=[('y', 'Y')])
 
     def init_grid_data(self):
-        self.grid_xs = [0, 1]
-        self.grid_ys = [0.1, 0.2, 0.3]
-        self.grid_zs = [[0, 1], [2, 3], [4, 5]]
+        self.grid_xs = np.array([0, 1])
+        self.grid_ys = np.array([0.1, 0.2, 0.3])
+        self.grid_zs = np.array([[0, 1], [2, 3], [4, 5]])
         self.dataset_grid = self.eltype((self.grid_xs, self.grid_ys,
                                          self.grid_zs), kdims=['x', 'y'],
                                         vdims=['z'])

From 969c06cc017614844d015729729e0c9c0876512d Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 17:28:18 +0100
Subject: [PATCH 08/20] Implemented Image.sample on top of ndloc interface

---
 holoviews/core/data/__init__.py |  4 ++-
 holoviews/element/raster.py     | 46 +++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index f5be2c39bc..8966efb682 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -433,7 +433,9 @@ def sample(self, samples=[], closest=True, **kwargs):
             else:
                 selection = tuple(selection.columns(kdims+self.vdims).values())
 
-            return self.clone(selection, kdims=kdims, new_type=new_type)
+            datatype = list(util.unique_iterator(self.datatype+['dataframe', 'dict']))
+            return self.clone(selection, kdims=kdims, new_type=new_type,
+                              datatype=datatype)
 
         lens = set(len(util.wrap_tuple(s)) for s in samples)
         if len(lens) > 1:
diff --git a/holoviews/element/raster.py b/holoviews/element/raster.py
index d4c3e58fab..93a4d6fd03 100644
--- a/holoviews/element/raster.py
+++ b/holoviews/element/raster.py
@@ -326,6 +326,52 @@ def select(self, selection_specs=None, **selection):
                               ydensity=self.ydensity, bounds=bounds)
 
 
+    def sample(self, samples=[], **kwargs):
+        """
+        Allows sampling of an Image as an iterator of coordinates
+        matching the key dimensions, returning a new object containing
+        just the selected samples. Alternatively may supply kwargs to
+        sample a coordinate on an object. On an Image the coordinates
+        are continuously indexed and will always snap to the nearest
+        coordinate.
+        """
+        if kwargs and samples:
+            raise Exception('Supply explicit list of samples or kwargs, not both.')
+        elif kwargs:
+            sample = [slice(None) for _ in range(self.ndims)]
+            for dim, val in kwargs.items():
+                sample[self.get_dimension_index(dim)] = val
+            samples = [tuple(sample)]
+
+        # If a 1D cross-section of 2D space return Curve
+        if len(samples) == 1:
+            dims = [kd for kd, v in zip(self.kdims, samples[0]) if not np.isscalar(v)]
+            if len(dims) == 1:
+                kdims = [self.get_dimension(kd) for kd in dims]
+                sel = {kd.name: s for kd, s in zip(self.kdims, samples[0])}
+                dims = [kd for kd, v in sel.items() if not np.isscalar(v)]
+                selection = self.select(**sel)
+                selection = tuple(selection.columns(kdims+self.vdims).values())
+                datatype = list(util.unique_iterator(self.datatype+['dataframe', 'dict']))
+                return self.clone(selection, kdims=kdims, new_type=Curve,
+                                  datatype=datatype)
+            else:
+                new_type = Table
+                kdims = self.kdims
+        else:
+            new_type = Dataset
+            kdims = self.kdims
+
+        xs, ys = [], []
+        for s in samples:
+            if len(s) > 1:
+                y, x = self.sheet2matrixidx(*s)
+                xs.append(x)
+                ys.append(y)
+        data = self.interface.ndloc(self, (ys, xs))
+        return self.clone(data, new_type=Dataset, datatype=['dataframe', 'dict'])
+
+
     def closest(self, coords=[], **kwargs):
         """
         Given a single coordinate or multiple coordinates as

From 2b727850415ff4254698726732e6086cd116e3e8 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 18:55:55 +0100
Subject: [PATCH 09/20] Fixed bug in Dataset unit test setup

---
 tests/testdataset.py | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tests/testdataset.py b/tests/testdataset.py
index 4d7d10345b..4822b84709 100644
--- a/tests/testdataset.py
+++ b/tests/testdataset.py
@@ -872,7 +872,8 @@ def setUp(self):
         self.restore_datatype = Dataset.datatype
         Dataset.datatype = ['grid']
         self.data_instance_type = dict
-        self.init_data()
+        self.init_column_data()
+        self.init_grid_data()
 
     def init_column_data(self):
         self.xs = np.arange(11)
@@ -1308,10 +1309,10 @@ class XArrayDaskArrayDatasetTest(XArrayDatasetTest):
 
     def init_column_data(self):
         import dask.array
-        self.xs = range(11)
-        self.xs_2 = [el**2 for el in self.xs]
+        self.xs = np.array(range(11))
+        self.xs_2 = self.xs**2
 
-        self.y_ints = [i*2 for i in range(11)]
+        self.y_ints = self.xs*2
         dask_y = dask.array.from_array(np.array(self.y_ints), 2)
         self.dataset_hm = Dataset((self.xs, dask_y),
                                   kdims=['x'], vdims=['y'])

From 9638fb892abfc615ed2d1d5edc40973330f305cb Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 19:01:54 +0100
Subject: [PATCH 10/20] Fixed closest bug in Image.sample

---
 holoviews/element/raster.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/holoviews/element/raster.py b/holoviews/element/raster.py
index 93a4d6fd03..adbfd7cf32 100644
--- a/holoviews/element/raster.py
+++ b/holoviews/element/raster.py
@@ -335,6 +335,7 @@ def sample(self, samples=[], **kwargs):
         are continuously indexed and will always snap to the nearest
         coordinate.
         """
+        kwargs = {k: v for k, v in kwargs.items() if k != 'closest'}
         if kwargs and samples:
             raise Exception('Supply explicit list of samples or kwargs, not both.')
         elif kwargs:

From 0da749b76618117fa9d03d23a00adb9a628ef75f Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 20:05:16 +0100
Subject: [PATCH 11/20] Fixed Image.sample y-coord index

---
 holoviews/element/raster.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/holoviews/element/raster.py b/holoviews/element/raster.py
index adbfd7cf32..fa7e241179 100644
--- a/holoviews/element/raster.py
+++ b/holoviews/element/raster.py
@@ -345,6 +345,7 @@ def sample(self, samples=[], **kwargs):
             samples = [tuple(sample)]
 
         # If a 1D cross-section of 2D space return Curve
+        shape = self.interface.shape(self, gridded=True)
         if len(samples) == 1:
             dims = [kd for kd, v in zip(self.kdims, samples[0]) if not np.isscalar(v)]
             if len(dims) == 1:
@@ -368,9 +369,9 @@ def sample(self, samples=[], **kwargs):
             if len(s) > 1:
                 y, x = self.sheet2matrixidx(*s)
                 xs.append(x)
-                ys.append(y)
+                ys.append(shape[0]-y)
         data = self.interface.ndloc(self, (ys, xs))
-        return self.clone(data, new_type=Dataset, datatype=['dataframe', 'dict'])
+        return self.clone(data, new_type=Table, datatype=['dataframe', 'dict'])
 
 
     def closest(self, coords=[], **kwargs):

From 4af6c8c098db0b0e3db81249c3f4b95fae26002a Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 21:27:13 +0100
Subject: [PATCH 12/20] Minor fixes for sampling

---
 doc/Tutorials/Introduction.ipynb | 2 +-
 holoviews/element/raster.py      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/doc/Tutorials/Introduction.ipynb b/doc/Tutorials/Introduction.ipynb
index 237b10a1a9..38e14b72cc 100644
--- a/doc/Tutorials/Introduction.ipynb
+++ b/doc/Tutorials/Introduction.ipynb
@@ -550,7 +550,7 @@
    "source": [
     "print(rgb_parrot)\n",
     "print(rgb_parrot[0,0])\n",
-    "print(rgb_parrot[0,0][0])"
+    "print(rgb_parrot[0,0].iloc[0, 0])"
    ]
   },
   {
diff --git a/holoviews/element/raster.py b/holoviews/element/raster.py
index fa7e241179..af805d9fcc 100644
--- a/holoviews/element/raster.py
+++ b/holoviews/element/raster.py
@@ -369,7 +369,7 @@ def sample(self, samples=[], **kwargs):
             if len(s) > 1:
                 y, x = self.sheet2matrixidx(*s)
                 xs.append(x)
-                ys.append(shape[0]-y)
+                ys.append(shape[0]-y-1)
         data = self.interface.ndloc(self, (ys, xs))
         return self.clone(data, new_type=Table, datatype=['dataframe', 'dict'])
 

From 3f5ba0509b3a7d6405d3d5ce5831b32df59be7d0 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 22:17:05 +0100
Subject: [PATCH 13/20] Added Image sampling test

---
 tests/testimageinterfaces.py | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tests/testimageinterfaces.py b/tests/testimageinterfaces.py
index 698ef195b7..9e6924b5b5 100644
--- a/tests/testimageinterfaces.py
+++ b/tests/testimageinterfaces.py
@@ -2,7 +2,7 @@
 from nose.plugins.attrib import attr
 
 import numpy as np
-from holoviews import Dimension, Image, Curve, RGB, HSV, Dataset
+from holoviews import Dimension, Image, Curve, RGB, HSV, Dataset, Table
 from holoviews.element.comparison import ComparisonTestCase
 
 from .testdataset import DatatypeContext
@@ -118,6 +118,18 @@ def test_sample_ycoord(self):
             self.assertEqual(self.image.sample(y=5),
                              Curve((xs, zs), kdims=['x'], vdims=['z']))
 
+    def test_sample_coords(self):
+        arr = np.arange(10)*np.arange(5)[np.newaxis].T
+        xs = np.linspace(0.12, 0.81, 10)
+        ys = np.linspace(0.12, 0.391, 5)
+        img = Image((xs, ys, arr), kdims=['x', 'y'], vdims=['z'], datatype=[self.datatype])
+        sampled = img.sample([(0.15, 0.15), (0.15, 0.4), (0.8, 0.4), (0.8, 0.15)])
+        self.assertIsInstance(sampled, Table)
+        yidx = [0, 4, 4, 0]
+        xidx = [0, 0, 9, 9]
+        table = Table((xs[xidx], ys[yidx], arr[yidx, xidx]), kdims=['x', 'y'], vdims=['z'])
+        self.assertEqual(sampled, table)
+
     def test_reduce_to_scalar(self):
         self.assertEqual(self.image.reduce(['x', 'y'], function=np.mean),
                          20.25)

From 788cea806401e5cb20b3685b38caa479072c4d98 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 23:00:47 +0100
Subject: [PATCH 14/20] Small fix for ndloc

---
 holoviews/core/data/interface.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/holoviews/core/data/interface.py b/holoviews/core/data/interface.py
index 6c0a49ae14..c34c828cac 100644
--- a/holoviews/core/data/interface.py
+++ b/holoviews/core/data/interface.py
@@ -66,12 +66,10 @@ def __getitem__(self, indices):
         selected = self.dataset.interface.ndloc(ds, indices)
         if np.isscalar(selected):
             return selected
-        datatype = [dt for dt in ds.datatype if dt in Interface.interfaces and
-                    Interface.interfaces[dt].gridded]
         params = {}
         if hasattr(ds, 'bounds'):
             params['bounds'] = None
-        return self.dataset.clone(selected, datatype=[ds.interface.datatype]+datatype, **params)
+        return self.dataset.clone(selected, datatype=[ds.interface.datatype]+ds.datatype, **params)
 
 
 class Interface(param.Parameterized):

From bdf2ad310505593507d0c941a548d79a900b28ca Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 23:01:24 +0100
Subject: [PATCH 15/20] Vectorized Image.sample

---
 holoviews/element/raster.py | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/holoviews/element/raster.py b/holoviews/element/raster.py
index af805d9fcc..cb07d6ebbd 100644
--- a/holoviews/element/raster.py
+++ b/holoviews/element/raster.py
@@ -364,13 +364,10 @@ def sample(self, samples=[], **kwargs):
             new_type = Dataset
             kdims = self.kdims
 
-        xs, ys = [], []
-        for s in samples:
-            if len(s) > 1:
-                y, x = self.sheet2matrixidx(*s)
-                xs.append(x)
-                ys.append(shape[0]-y-1)
-        data = self.interface.ndloc(self, (ys, xs))
+        xs, ys = zip(*samples)
+        yidx, xidx = self.sheet2matrixidx(np.array(xs), np.array(ys))
+        yidx = shape[0]-yidx-1
+        data = self.interface.ndloc(self, (yidx, xidx))
         return self.clone(data, new_type=Table, datatype=['dataframe', 'dict'])
 
 

From 6571609d4fc2f19a046fff5cfa22b78c8fc5c79d Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 23:01:52 +0100
Subject: [PATCH 16/20] Added ndloc unit tests

---
 tests/testdataset.py | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/tests/testdataset.py b/tests/testdataset.py
index 4822b84709..56af76ef4a 100644
--- a/tests/testdataset.py
+++ b/tests/testdataset.py
@@ -911,6 +911,44 @@ def test_canonical_vdim(self):
         self.assertEqual(dataset.dimension_values('z', flat=False),
                          canonical)
 
+    def test_dataset_ndloc_index(self):
+        xs, ys = np.linspace(0.12, 0.81, 10), np.linspace(0.12, 0.391, 5)
+        arr = np.arange(10)*np.arange(5)[np.newaxis].T
+        ds = Dataset((xs, ys, arr), kdims=['x', 'y'], vdims=['z'], datatype=[self.datatype])
+        self.assertEqual(ds.ndloc[0,0], arr[0, 0])
+
+    def test_dataset_ndloc_index2(self):
+        xs, ys = np.linspace(0.12, 0.81, 10), np.linspace(0.12, 0.391, 5)
+        arr = np.arange(10)*np.arange(5)[np.newaxis].T
+        ds = Dataset((xs, ys, arr), kdims=['x', 'y'], vdims=['z'], datatype=[self.datatype])
+        self.assertEqual(ds.ndloc[4, 9], arr[4, 9])
+
+    def test_dataset_ndloc_slice(self):
+        xs, ys = np.linspace(0.12, 0.81, 10), np.linspace(0.12, 0.391, 5)
+        arr = np.arange(10)*np.arange(5)[np.newaxis].T
+        ds = Dataset((xs, ys, arr), kdims=['x', 'y'], vdims=['z'], datatype=[self.datatype])
+        sliced = Dataset((xs[2:5], ys[1:], arr[1:, 2:5]), kdims=['x', 'y'], vdims=['z'],
+                         datatype=[self.datatype])
+        self.assertEqual(ds.ndloc[1:, 2:5], sliced)
+
+    def test_dataset_ndloc_lists(self):
+        xs, ys = np.linspace(0.12, 0.81, 10), np.linspace(0.12, 0.391, 5)
+        arr = np.arange(10)*np.arange(5)[np.newaxis].T
+        ds = Dataset((xs, ys, arr), kdims=['x', 'y'], vdims=['z'], datatype=[self.datatype, 'dictionary'])
+        sliced = Dataset((xs[[1, 2, 3]], ys[[0, 1, 2]], arr[[0, 1, 2], [1, 2, 3]]), kdims=['x', 'y'], vdims=['z'],
+                         datatype=['dictionary'])
+        self.assertEqual(ds.ndloc[[0, 1, 2], [1, 2, 3]], sliced)
+
+    def test_dataset_ndloc_slice_two_vdims(self):
+        xs, ys = np.linspace(0.12, 0.81, 10), np.linspace(0.12, 0.391, 5)
+        arr = np.arange(10)*np.arange(5)[np.newaxis].T
+        arr2 = (np.arange(10)*np.arange(5)[np.newaxis].T)[::-1]
+        ds = Dataset((xs, ys, arr, arr2), kdims=['x', 'y'], vdims=['z', 'z2'], datatype=[self.datatype, 'dictionary'])
+        sliced = Dataset((xs[[1, 2, 3]], ys[[0, 1, 2]], arr[[0, 1, 2], [1, 2, 3]],
+                          arr2[[0, 1, 2], [1, 2, 3]]), kdims=['x', 'y'], vdims=['z', 'z2'],
+                         datatype=['dictionary'])
+        self.assertEqual(ds.ndloc[[0, 1, 2], [1, 2, 3]], sliced)
+
     def test_dataset_dim_vals_grid_kdims_xs(self):
         self.assertEqual(self.dataset_grid.dimension_values(0, expanded=False),
                          np.array([0, 1]))
@@ -1248,6 +1286,9 @@ def test_dataset_groupby_drop_dims_with_vdim(self):
     def test_dataset_groupby_drop_dims_dynamic_with_vdim(self):
         raise SkipTest("Not supported")
 
+    def test_dataset_ndloc_slice_two_vdims(self):
+        raise SkipTest("Not supported")
+
 
 @attr(optional=1)
 class XArrayDatasetTest(GridDatasetTest):

From 8607c20bd83f7f1da0afa579c775f2a94139a792 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 23:27:51 +0100
Subject: [PATCH 17/20] Simplified decimate operation using iloc

---
 holoviews/operation/element.py | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/holoviews/operation/element.py b/holoviews/operation/element.py
index 7530791dfe..47bc2d00ae 100644
--- a/holoviews/operation/element.py
+++ b/holoviews/operation/element.py
@@ -597,17 +597,7 @@ def _process_layer(self, element, key=None):
 
         if len(sliced) > self.p.max_samples:
             prng = np.random.RandomState(self.p.random_seed)
-            length = len(sliced)
-            if element.interface is PandasInterface:
-                data = sliced.data.sample(self.p.max_samples,
-                                          random_state=prng)
-            else:
-                inds = prng.choice(length, self.p.max_samples, False)
-                if isinstance(element.interface, DictInterface):
-                    data = {k: v[inds] for k, v in sliced.data.items()}
-                else:
-                    data = sliced.data[inds, :]
-            sliced = element.clone(data)
+            return element.iloc[prng.choice(len(sliced), self.p.max_samples, False)]
         return sliced
 
     def _process(self, element, key=None):

From 922accd701e5b122f6a97c5ddd96f646f022d4cb Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Sun, 18 Jun 2017 23:37:00 +0100
Subject: [PATCH 18/20] Use iloc in Tabular.pprint_cell

---
 holoviews/core/element.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/holoviews/core/element.py b/holoviews/core/element.py
index 55bfd64f52..1e424c5375 100644
--- a/holoviews/core/element.py
+++ b/holoviews/core/element.py
@@ -228,8 +228,7 @@ def pprint_cell(self, row, col):
             return self.kdims[col].pprint_label
         else:
             dim = self.get_dimension(col)
-            values = self[dim.name]
-            return dim.pprint_value(values[row-1])
+            return dim.pprint_value(self.iloc[row-1, col])
 
 
     def cell_type(self, row, col):

From 5a1d93062dd87c21ef57eaefd77968a056a6516c Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Mon, 19 Jun 2017 00:34:08 +0100
Subject: [PATCH 19/20] Improved iloc and ndloc docstrings

---
 holoviews/core/data/__init__.py  | 46 +++++++++++++++++++++++++++++---
 holoviews/core/data/interface.py | 10 ++++++-
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index 8966efb682..d8d2836483 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -629,16 +629,54 @@ def to(self):
     @property
     def iloc(self):
         """
-        Returns an iloc object, providing a convenient interface to
-        slice and index into the Dataset using row and column indices,
-        allow selection by integer index, slice and list of integer
-        indices and boolean arrays.
+        Returns an iloc object providing a convenient interface to
+        slice and index into the Dataset using row and column indices.
+        Allow selection by integer index, slice and list of integer
+        indices and boolean arrays, e.g.:
+
+        Examples:
+
+        * Index the first row and column:
+
+            dataset.iloc[0, 0]
+
+        * Select rows 1 and 2 with a slice:
+
+            dataset.iloc[1:3, :]
+
+        * Select with a list of integer coordinates:
+
+            dataset.iloc[[0, 2, 3]]
         """
         return iloc(self)
 
 
     @property
     def ndloc(self):
+        """
+        Returns an ndloc object providing nd-array like indexing for
+        gridded datasets. Follows NumPy array indexing conventions,
+        allowing for indexing, slicing and selecting a list of indices
+        on multi-dimensional arrays using integer indices. The order
+        of array indices is inverted Dataset key dimensions, e.g. an
+        Image with key dimensions 'x' and 'y' can be indexed with
+        ``image.ndloc[iy, ix]``, where ``iy`` and ``ix`` are integer
+        indices along the y and x dimensions.
+
+        Examples:
+
+        * Index value in 2D array:
+
+            dataset.ndloc[3, 1]
+
+        * Slice along y-axis of 2D array:
+
+            dataset.ndloc[2:5, :]
+
+        * Select with integer coordinates along x- and y-axes:
+
+            dataset.ndloc[[1, 2, 3], [0, 2, 3]]
+        """
         return ndloc(self)
 
 
diff --git a/holoviews/core/data/interface.py b/holoviews/core/data/interface.py
index c34c828cac..8694e95260 100644
--- a/holoviews/core/data/interface.py
+++ b/holoviews/core/data/interface.py
@@ -11,7 +11,8 @@ class iloc(object):
     iloc is small wrapper object that allows row, column based
     indexing into a Dataset using the ``.iloc`` property.  It supports
     the usual numpy and pandas iloc indexing semantics including
-    integer indices, slices, lists and arrays of values.
+    integer indices, slices, lists and arrays of values. For more
+    information see the ``Dataset.iloc`` property docstring.
     """
 
     def __init__(self, dataset):
@@ -54,6 +55,13 @@ def __getitem__(self, index):
 
 
 class ndloc(object):
+    """
+    ndloc is a small wrapper object that allows ndarray-like indexing
+    for gridded Datasets using the ``.ndloc`` property. It supports
+    the standard NumPy ndarray indexing semantics including
+    integer indices, slices, lists and arrays of values. For more
+    information see the ``Dataset.ndloc`` property docstring.
+    """
 
     def __init__(self, dataset):
         self.dataset = dataset

From 3ecff25bc06acc8c1487e364204f22dd90257607 Mon Sep 17 00:00:00 2001
From: Philipp Rudiger <P.Rudiger@ed.ac.uk>
Date: Mon, 19 Jun 2017 02:13:36 +0100
Subject: [PATCH 20/20] Small docstring fixes for iloc and ndloc

---
 holoviews/core/data/__init__.py | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index d8d2836483..4944bb4780 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -632,7 +632,7 @@ def iloc(self):
         Returns an iloc object providing a convenient interface to
         slice and index into the Dataset using row and column indices.
         Allow selection by integer index, slice and list of integer
-        indices and boolean arrays, e.g.:
+        indices and boolean arrays.
 
         Examples:
 
@@ -658,10 +658,10 @@ def ndloc(self):
         gridded datasets. Follows NumPy array indexing conventions,
         allowing for indexing, slicing and selecting a list of indices
         on multi-dimensional arrays using integer indices. The order
-        of array indices is inverted Dataset key dimensions, e.g. an
-        Image with key dimensions 'x' and 'y' can be indexed with
-        ``image.ndloc[iy, ix]``, where ``iy`` and ``ix`` are integer
-        indices along the y and x dimensions.
+        of array indices is inverted relative to the Dataset key
+        dimensions, e.g. an Image with key dimensions 'x' and 'y' can
+        be indexed with ``image.ndloc[iy, ix]``, where ``iy`` and
+        ``ix`` are integer indices along the y and x dimensions.
 
         Examples:
 
@@ -673,7 +673,7 @@ def ndloc(self):
 
             dataset.ndloc[2:5, :]
 
-        * Select with integer coordinates along x- and y-axes:
+        * Vectorized (non-orthogonal) indexing along x- and y-axes:
 
             dataset.ndloc[[1, 2, 3], [0, 2, 3]]
         """