ENH: Add (put|take)_along_axis as described in #8708

This is the reduced version that does not allow any insertion of extra dimensions

1 files changed, 91 insertions, 1 deletions

diff --git a/numpy/lib/tests/test_shape_base.py b/numpy/lib/tests/test_shape_base.py
index a35d90b70..c95894f94 100644
--- a/numpy/lib/tests/test_shape_base.py
+++ b/numpy/lib/tests/test_shape_base.py
@@ -2,16 +2,106 @@ from __future__ import division, absolute_import, print_function
 
 import numpy as np
 import warnings
+import functools
 
 from numpy.lib.shape_base import (
     apply_along_axis, apply_over_axes, array_split, split, hsplit, dsplit,
-    vsplit, dstack, column_stack, kron, tile, expand_dims,
+    vsplit, dstack, column_stack, kron, tile, expand_dims, take_along_axis,
+    put_along_axis
     )
 from numpy.testing import (
     assert_, assert_equal, assert_array_equal, assert_raises, assert_warns
     )
 
 
+def _add_keepdims(func):
+    """ hack in keepdims behavior into a function taking an axis """
+    @functools.wraps(func)
+    def wrapped(a, axis, **kwargs):
+        res = func(a, axis=axis, **kwargs)
+        if axis is None:
+            axis = 0  # res is now a scalar, so we can insert this anywhere
+        return np.expand_dims(res, axis=axis)
+    return wrapped
+
+
+class TestTakeAlongAxis(object):
+    def test_argequivalent(self):
+        """ Test it translates from arg<func> to <func> """
+        from numpy.random import rand
+        a = rand(3, 4, 5)
+
+        funcs = [
+            (np.sort, np.argsort, dict()),
+            (_add_keepdims(np.min), _add_keepdims(np.argmin), dict()),
+            (_add_keepdims(np.max), _add_keepdims(np.argmax), dict()),
+            (np.partition, np.argpartition, dict(kth=2)),
+        ]
+
+        for func, argfunc, kwargs in funcs:
+            for axis in list(range(a.ndim)) + [None]:
+                a_func = func(a, axis=axis, **kwargs)
+                ai_func = argfunc(a, axis=axis, **kwargs)
+                assert_equal(a_func, take_along_axis(a, ai_func, axis=axis))
+
+    def test_invalid(self):
+        """ Test it errors when indices has too few dimensions """
+        a = np.ones((10, 10))
+        ai = np.ones((10, 2), dtype=np.intp)
+
+        # sanity check
+        take_along_axis(a, ai, axis=1)
+
+        # not enough indices
+        assert_raises(ValueError, take_along_axis, a, np.array(1), axis=1)
+        # bool arrays not allowed
+        assert_raises(IndexError, take_along_axis, a, ai.astype(bool), axis=1)
+        # float arrays not allowed
+        assert_raises(IndexError, take_along_axis, a, ai.astype(float), axis=1)
+        # invalid axis
+        assert_raises(np.AxisError, take_along_axis, a, ai, axis=10)
+
+    def test_empty(self):
+        """ Test everything is ok with empty results, even with inserted dims """
+        a  = np.ones((3, 4, 5))
+        ai = np.ones((3, 0, 5), dtype=np.intp)
+
+        actual = take_along_axis(a, ai, axis=1)
+        assert_equal(actual.shape, ai.shape)
+
+    def test_broadcast(self):
+        """ Test that non-indexing dimensions are broadcast in both directions """
+        a  = np.ones((3, 4, 1))
+        ai = np.ones((1, 2, 5), dtype=np.intp)
+        actual = take_along_axis(a, ai, axis=1)
+        assert_equal(actual.shape, (3, 2, 5))
+
+
+class TestPutAlongAxis(object):
+    def test_replace_max(self):
+        a_base = np.array([[10, 30, 20], [60, 40, 50]])
+
+        for axis in list(range(a_base.ndim)) + [None]:
+            # we mutate this in the loop
+            a = a_base.copy()
+
+            # replace the max with a small value
+            i_max = _add_keepdims(np.argmax)(a, axis=axis)
+            put_along_axis(a, i_max, -99, axis=axis)
+
+            # find the new minimum, which should max
+            i_min = _add_keepdims(np.argmin)(a, axis=axis)
+
+            assert_equal(i_min, i_max)
+
+    def test_broadcast(self):
+        """ Test that non-indexing dimensions are broadcast in both directions """
+        a  = np.ones((3, 4, 1))
+        ai = np.arange(10, dtype=np.intp).reshape((1, 2, 5)) % 4
+        put_along_axis(a, ai, 20, axis=1)
+        assert_equal(take_along_axis(a, ai, axis=1), 20)
+
+
 class TestApplyAlongAxis(object):
     def test_simple(self):
         a = np.ones((20, 10), 'd')