fix(api): ensure the order of duplicate non-renamed columns in `reloc…

…ate` is preserved

ibis/expr/types/relations.py

@@ -3898,6 +3898,33 @@ def relocate(
         ├───────┼───────┼────────┼────────┤
         │     1 │     1 │ a      │ a      │
         └───────┴───────┴────────┴────────┘
+
+        When there are duplicate **renames** in a call to relocate, the
+        last one is preserved
+
+        >>> t.relocate(e="d", f="d")
+        ┏━━━━━━━━┳━━━━━━━┳━━━━━━━━┳━━━━━━━┓
+        ┃ f      ┃ a     ┃ b      ┃ c     ┃
+        ┡━━━━━━━━╇━━━━━━━╇━━━━━━━━╇━━━━━━━┩
+        │ string │ int64 │ string │ int64 │
+        ├────────┼───────┼────────┼───────┤
+        │ a      │     1 │ a      │     1 │
+        └────────┴───────┴────────┴───────┘
+
+        However, if there are duplicates that are **not** part of a rename, the
+        order specified in the relocate call is preserved
+
+        >>> t.relocate(
+        ...     "b",
+        ...     s.of_type("string"),  # "b" is a string column, so the selector matches
+        ... )
+        ┏━━━━━━━━┳━━━━━━━━┳━━━━━━━┳━━━━━━━┓
+        ┃ b      ┃ d      ┃ a     ┃ c     ┃
+        ┡━━━━━━━━╇━━━━━━━━╇━━━━━━━╇━━━━━━━┩
+        │ string │ string │ int64 │ int64 │
+        ├────────┼────────┼───────┼───────┤
+        │ a      │ a      │     1 │     1 │
+        └────────┴────────┴───────┴───────┘
         """
         import ibis.selectors as s
 
@@ -3917,11 +3944,13 @@ def relocate(
             zip(kwargs.keys(), map(s._to_selector, kwargs.values())),
         ):
             for pos in sel.positions(self):
-                if pos in sels:
-                    # make sure the last duplicate column wins by reinserting
-                    # the position if it already exists
+                renamed = name is not None
+                if pos in sels and renamed:
+                    # **only when renaming**: make sure the last duplicate
+                    # column wins by reinserting the position if it already
+                    # exists
                     del sels[pos]
-                sels[pos] = name if name is not None else table_columns[pos]
+                sels[pos] = name if renamed else table_columns[pos]
 
         ncols = len(table_columns)
 

ibis/tests/expr/test_relocate.py

@@ -19,6 +19,12 @@ def test_move_blocks():
     assert t.relocate(s.of_type("string"), after=s.numeric()).columns == list("xyab")
 
 
+def test_duplicates_not_renamed():
+    t = ibis.table(dict(x="int", y="int"))
+    assert t.relocate("y", s.numeric()).columns == list("yx")
+    assert t.relocate("y", s.numeric(), "y").columns == list("yx")
+
+
 def test_keep_non_contiguous_variables():
     t = ibis.table(dict.fromkeys("abcde", "int"))
     assert t.relocate("b", after=s.c("a", "c", "e")).columns == list("acdeb")