Implemented a function for smarter debug formatting.

src/arrayformat.rs

@@ -11,9 +11,203 @@ use super::{
     Data,
     Dimension,
     NdProducer,
+    Ix
 };
 use crate::dimension::IntoDimension;
 
+#[derive(Debug)]
+enum ArrayDisplayMode {
+    // Array is small enough to me printed without omitting any values.
+    Full,
+    // Omit central values of the nth axis. Since we print that axis horizontally, ellipses
+    // on each row do something like a split of the array into 2 parts vertically.
+    VSplit,
+    // Omit central values of the certain axis. Since we do it only once, ellipses on each row
+    // do something like a split of the array into 2 parts horizontally.
+    HSplit(Ix),
+    // Both `VSplit` and `HSplit` hold.
+    DoubleSplit(Ix),
+}
+
+const PRINT_ELEMENTS_LIMIT: Ix = 5;
+
+impl ArrayDisplayMode {
+    fn from_array<A, S, D>(arr: &ArrayBase<S, D>, limit: usize) -> ArrayDisplayMode
+        where S: Data<Elem=A>,
+              D: Dimension
+    {
+        let last_dim = match arr.shape().len().checked_sub(1) {
+            Some(v) => v,
+            None => {
+                return ArrayDisplayMode::Full;
+            }
+        };
+
+        let mut overflow_axis_pair: (Option<usize>, Option<usize>) = (None, None);
+        for (axis, axis_size) in arr.shape().iter().enumerate().rev() {
+            if *axis_size >= 2 * limit + 1 {
+                match overflow_axis_pair.0 {
+                    Some(_) => {
+                        if let None = overflow_axis_pair.1 {
+                            overflow_axis_pair.1 = Some(axis);
+                        }
+                    },
+                    None => {
+                        if axis != last_dim {
+                            return ArrayDisplayMode::HSplit(axis);
+                        }
+                        overflow_axis_pair.0 = Some(axis);
+                    }
+                }
+            }
+        }
+
+        match overflow_axis_pair {
+            (Some(_), Some(h_axis)) => ArrayDisplayMode::DoubleSplit(h_axis),
+            (Some(_), None) => ArrayDisplayMode::VSplit,
+            (None, _) => ArrayDisplayMode::Full,
+        }
+    }
+
+    fn h_split_offset(&self) -> Option<Ix> {
+        match self {
+            ArrayDisplayMode::DoubleSplit(axis) | ArrayDisplayMode::HSplit(axis) => {
+                Some(axis + 1usize)
+            },
+            _ => None
+        }
+    }
+}
+
+fn format_array_v2<A, S, D, F>(view: &ArrayBase<S, D>,
+                                  f: &mut fmt::Formatter,
+                                  mut format: F,
+                                  limit: usize) -> fmt::Result
+    where F: FnMut(&A, &mut fmt::Formatter) -> fmt::Result,
+          D: Dimension,
+          S: Data<Elem=A>,
+{
+    let display_mode = ArrayDisplayMode::from_array(view, limit);
+
+    let ndim = view.dim().into_dimension().slice().len();
+    let nth_idx_max = if ndim > 0 { Some(view.shape().iter().last().unwrap()) } else { None };
+
+    // None will be an empty iter.
+    let mut last_index = match view.dim().into_dimension().first_index() {
+        None => view.dim().into_dimension().clone(),
+        Some(ix) => ix,
+    };
+    for _ in 0..ndim {
+        write!(f, "[")?;
+    }
+    let mut first = true;
+    // Shows if ellipses for vertical split were printed.
+    let mut printed_ellipses_v = false;
+    // Shows if ellipses for horizontal split were printed.
+    let mut printed_ellipses_h = false;
+    // Shows if the row was printed for the first time after horizontal split.
+    let mut no_rows_after_skip_yet = false;
+
+    // Simply use the indexed iterator, and take the index wraparounds
+    // as cues for when to add []'s and how many to add.
+    for (index, elt) in view.indexed_iter() {
+        let index = index.into_dimension();
+        let take_n = if ndim == 0 { 1 } else { ndim - 1 };
+        let mut update_index = false;
+
+        let mut print_row = true;
+        match display_mode {
+            ArrayDisplayMode::HSplit(axis) | ArrayDisplayMode::DoubleSplit(axis) => {
+                let sa_idx_max = view.shape().iter().skip(axis).next().unwrap();
+                let sa_idx_val = index.slice().iter().skip(axis).next().unwrap();
+                if sa_idx_val >= &limit && sa_idx_val < &(sa_idx_max - &limit) {
+                    print_row = false;
+                    no_rows_after_skip_yet = true;
+                }
+            },
+            _ => {}
+        }
+
+        for (i, (a, b)) in index.slice()
+            .iter()
+            .take(take_n)
+            .zip(last_index.slice().iter())
+            .enumerate() {
+            if a != b {
+                if print_row {
+                    printed_ellipses_v = false;
+                    // New row.
+                    // # of ['s needed
+                    let n = ndim - i - 1;
+                    if !no_rows_after_skip_yet {
+                        for _ in 0..n {
+                            write!(f, "]")?;
+                        }
+                        write!(f, ",")?;
+                        write!(f, "\n")?;
+                    }
+                    no_rows_after_skip_yet = false;
+                    for _ in 0..ndim - n {
+                        write!(f, " ")?;
+                    }
+                    for _ in 0..n {
+                        write!(f, "[")?;
+                    }
+                } else if !printed_ellipses_h {
+                    let n = ndim - i - 1;
+                    for _ in 0..n {
+                        write!(f, "]")?;
+                    }
+                    write!(f, ",")?;
+                    write!(f, "\n")?;
+                    for _ in 0..display_mode.h_split_offset().unwrap() {
+                        write!(f, " ")?;
+                    }
+                    write!(f, "...,\n")?;
+                    printed_ellipses_h = true;
+                }
+                first = true;
+                update_index = true;
+                break;
+            }
+        }
+
+        if print_row {
+            let mut print_elt = true;
+            let nth_idx_op = index.slice().iter().last();
+            match display_mode {
+                ArrayDisplayMode::VSplit | ArrayDisplayMode::DoubleSplit(_) => {
+                    let nth_idx_val = nth_idx_op.unwrap();
+                    if nth_idx_val >= &limit && nth_idx_val < &(nth_idx_max.unwrap() - &limit) {
+                        print_elt = false;
+                        if !printed_ellipses_v {
+                            write!(f, ", ...")?;
+                            printed_ellipses_v = true;
+                        }
+                    }
+                }
+                _ => {}
+            }
+
+            if print_elt {
+                if !first {
+                    write!(f, ", ")?;
+                }
+                first = false;
+                format(elt, f)?;
+            }
+        }
+
+        if update_index {
+            last_index = index;
+        }
+    }
+    for _ in 0..ndim {
+        write!(f, "]")?;
+    }
+    Ok(())
+}
+
 fn format_array<A, S, D, F>(view: &ArrayBase<S, D>, f: &mut fmt::Formatter,
                             mut format: F)
     -> fmt::Result
@@ -92,7 +286,7 @@ impl<'a, A: fmt::Display, S, D: Dimension> fmt::Display for ArrayBase<S, D>
     where S: Data<Elem=A>,
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        format_array(self, f, <_>::fmt)
+        format_array_v2(self, f, <_>::fmt, PRINT_ELEMENTS_LIMIT)
     }
 }
 
@@ -105,7 +299,7 @@ impl<'a, A: fmt::Debug, S, D: Dimension> fmt::Debug for ArrayBase<S, D>
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         // Add extra information for Debug
-        format_array(self, f, <_>::fmt)?;
+        format_array_v2(self, f, <_>::fmt, PRINT_ELEMENTS_LIMIT)?;
         write!(f, " shape={:?}, strides={:?}, layout={:?}",
                self.shape(), self.strides(), layout=self.view().layout())?;
         match D::NDIM {