Merge pull request #2821 from ContinuumIO/ufunc-fancy-indexing3

in place fancy indexing for ufuncs

1 files changed, 53 insertions, 0 deletions

diff --git a/numpy/add_newdocs.py b/numpy/add_newdocs.py
index 5bb800488..65a416a9f 100644
--- a/numpy/add_newdocs.py
+++ b/numpy/add_newdocs.py
@@ -5815,6 +5815,59 @@ add_newdoc('numpy.core', 'ufunc', ('outer',
 
     """))
 
+add_newdoc('numpy.core', 'ufunc', ('at',
+    """
+    at(a, indices, b=None)
+
+    Performs unbuffered in place operation on operand 'a' for elements
+    specified by 'indices'. For addition ufunc, this method is equivalent to
+    `a[indices] += b`, except that results are accumulated for elements that
+    are indexed more than once. For example, `a[[0,0]] += 1` will only
+    increment the first element once because of buffering, whereas
+    `add.at(a, [0,0], 1)` will increment the first element twice.
+
+    Parameters
+    ----------
+    a : array_like
+        The array to perform in place operation on.
+    indices : array_like or tuple
+        Array like index object or slice object for indexing into first
+        operand. If first operand has multiple dimensions, indices can be a
+        tuple of array like index objects or slice objects.
+    b : array_like
+        Second operand for ufuncs requiring two operands. Operand must be
+        broadcastable over first operand after indexing or slicing.
+
+    Examples
+    --------
+    Set items 0 and 1 to their negative values:
+
+    >>> a = np.array([1, 2, 3, 4])
+    >>> np.negative.at(a, [0, 1])
+    >>> print(a)
+    array([-1, -2, 3, 4])
+
+    ::
+
+    Increment items 0 and 1, and increment item 2 twice:
+
+    >>> a = np.array([1, 2, 3, 4])
+    >>> np.add.at(a, [0, 1, 2, 2], 1)
+    >>> print(a)
+    array([2, 3, 5, 4])
+
+    ::
+
+    Add items 0 and 1 in first array to second array,
+    and store results in first array:
+
+    >>> a = np.array([1, 2, 3, 4])
+    >>> b = np.array([1, 2])
+    >>> np.add.at(a, [0, 1], b)
+    >>> print(a)
+    array([2, 4, 3, 4])
+
+    """))
 
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