8000 add extended axis and keepdims support to percentile and median by juliantaylor · Pull Request #3908 · numpy/numpy · GitHub
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add extended axis and keepdims support to percentile and median #3908

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merged 2 commits into from
Mar 13, 2014
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add extended axis and keepdims support to percentile and median #3908

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eea1a9c
ENH: add extended axis and keepdims support to median and percentile
juliantaylor Oct 13, 2013
7d53c81
MAINT: revert back to separate median implementation
juliantaylor Mar 12, 2014
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ENH: add extended axis and keepdims support to median and percentile
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@juliantaylor
juliantaylor committed Mar 13, 2014
commit eea1a9c49024c18fda3ad9782dee3956492cfa1a
165 changes: 113 additions & 52 deletions numpy/lib/function_base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
import warnings
import sys
import collections
import operator

import numpy as np
import numpy.core.numeric as _nx
Expand Down Expand Up @@ -2694,7 +2695,7 @@ def msort(a):
return b


def median(a, axis=None, out=None, overwrite_input=False):
def median(a, axis=None, out=None, overwrite_input=False, keepdims=False):
"""
Compute the median along the specified axis.

Expand All @@ -2704,9 +2705,10 @@ def median(a, axis=None, out=None, overwrite_input=False):
----------
a : array_like
Input array or object that can be converted to an array.
axis : int, optional
axis : int or sequence of int, optional
Axis along which the medians are computed. The default (axis=None)
is to compute the median along a flattened version of the array.
A sequence of axes is supported since version 1.9.0.
out : ndarray, optional
Alternative output array in which to place the result. It must have
the same shape and buffer length as the expected output, but the
Expand All @@ -2719,6 +2721,13 @@ def median(a, axis=None, out=None, overwrite_input=False):
will probably be fully or partially sorted. Default is False. Note
that, if `overwrite_input` is True and the input is not already an
ndarray, an error will be raised.
keepdims : bool, optional
If this is set to True, the axes which are reduced are left
in the result as dimensions with size one. With this option,
the result will broadcast correctly against the original `arr`.

.. versionadded:: 1.9.0


Returns
-------
Expand Down Expand Up @@ -2769,55 +2778,79 @@ def median(a, axis=None, out=None, overwrite_input=False):

"""
a = np.asanyarray(a)
if axis is not None and axis >= a.ndim:
raise IndexError(
"axis %d out of bounds (%d)" % (axis, a.ndim))

if overwrite_input:
if axis is None:
part = a.ravel()
sz = part.size
if sz % 2 == 0:
szh = sz // 2
part.partition((szh - 1, szh))
else:
part.partition((sz - 1) // 2)
else:
sz = a.shape[axis]
if sz % 2 == 0:
szh = sz // 2
a.partition((szh - 1, szh), axis=axis)
else:
a.partition((sz - 1) // 2, axis=axis)
part = a
if a.size % 2 == 0:
return percentile(a, q=50., axis=axis, out=out,
overwrite_input=overwrite_input,
interpolation="linear", keepdims=keepdims)
else:
if axis is None:
sz = a.size
else:
sz = a.shape[axis]
if sz % 2 == 0:
part = partition(a, ((sz // 2) - 1, sz // 2), axis=axis)
else:
part = partition(a, (sz - 1) // 2, axis=axis)
if part.shape == ():
# make 0-D arrays work
return part.item()
if axis is None:
axis = 0
indexer = [slice(None)] * part.ndim
index = part.shape[axis] // 2
if part.shape[axis] % 2 == 1:
# index with slice to allow mean (below) to work
indexer[axis] = slice(index, index+1)
# avoid slower weighting path, relevant for small arrays
return percentile(a, q=50., axis=axis, out=out,
overwrite_input=overwrite_input,
interpolation="nearest", keepdims=keepdims)


def _ureduce(a, func, **kwargs):
"""
Internal Function.
Call `func` with `a` as first argument swapping the axes to use extended
axis on functions that don't support it natively.

Returns result and a.shape with axis dims set to 1.

Parameters
----------
a : array_like
Input array or object that can be converted to an array.
func : callable
Reduction function Kapable of receiving an axis argument.
It is is called with `a` as first argument followed by `kwargs`.
kwargs : keyword arguments
additional keyword arguments to pass to `func`.

Returns
-------
result : tuple
Result of func(a, **kwargs) and a.shape with axis dims set to 1
suiteable to use to archive the same result as the ufunc keepdims
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suiteable <- suitable.

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archive <- achieve?

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fixed by reformulating the sentence

argument.

"""
a = np.asanyarray(a)
axis = kwargs.get('axis', None)
if axis is not None:
keepdim = list(a.shape)
nd = a.ndim
try:
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Could maybe simplify this, as axis=tuple(...) is currently the only alternative to a single integer.

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can you elaborate? I don't understand what you mean

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I was thinking just check for tuple instead of the try...except construct. But that is minor and the current approach might be safer.

axis = operator.index(axis)
if axis >= nd or axis < -nd:
raise IndexError("axis %d out of bounds (%d)" % (axis, a.ndim))
keepdim[axis] = 1
except TypeError:
sax = set()
for x in axis:
if x >= nd or x < -nd:
raise IndexError("axis %d out of bounds (%d)" % (x, nd))
if x in sax:
raise ValueError("duplicate value in axis")
sax.add(x % nd)
keepdim[x] = 1
keep = sax.symmetric_difference(frozenset(range(nd)))
nkeep = len(keep)
# swap axis that should not be reduced to front
for i, s in enumerate(sorted(keep)):
a = a.swapaxes(i, s)
# merge reduced axis
a = a.reshape(a.shape[:nkeep] + (-1,))
kwargs['axis'] = -1
else:
indexer[axis] = slice(index-1, index+1)
# Use mean in odd and even case to coerce data type
# and check, use out array.
return mean(part[indexer], axis=axis, out=out)
keepdim = [1] * a.ndim

r = func(a, **kwargs)
return r, keepdim


def percentile(a, q, axis=None, out=None,
overwrite_input=False, interpolation='linear'):
overwrite_input=False, interpolation='linear', keepdims=False):
"""
Compute the qth percentile of the data along the specified axis.

Expand All @@ -2829,9 +2862,10 @@ def percentile(a, q, axis=None, out=None,
Input array or object that can be converted to an array.
q : float in range of [0,100] (or sequence of floats)
Percentile to compute which must be between 0 and 100 inclusive.
axis : int, optional
axis : int or sequence of int, optional
Axis along which the percentiles are computed. The default (None)
is to compute the percentiles along a flattened version of the array.
A sequence of axes is supported since version 1.9.0.
out : ndarray, optional
Alternative output array in which to place the result. It must
have the same shape and buffer length as the expected output,
Expand All @@ -2857,6 +2891,12 @@ def percentile(a, q, axis=None, out=None,
* midpoint: (`i` + `j`) / 2.

.. versionadded:: 1.9.0
keepdims : bool, optional
If this is set to True, the axes which are reduced are left
in the result as dimensions with size one. With this option,
the result will broadcast correctly against the original `arr`.

.. versionadded:: 1.9.0

Returns
-------
Expand Down Expand Up @@ -2913,19 +2953,40 @@ def percentile(a, q, axis=None, out=None,
array([ 3.5])

"""
q = asarray(q, dtype=np.float64)
r, k = _ureduce(a, func=_percentile, q=q, axis=axis, out=out,
overwrite_input=overwrite_input,
interpolation=interpolation)
if keepdims:
if q.ndim == 0:
return r.reshape(k)
else:
return r.reshape([len(q)] + k)
else:
return r


def _percentile(a, q, axis=None, out=None,
overwrite_input=False, interpolation='linear', keepdims=False):
a = asarray(a)
q = asarray(q)
if q.ndim == 0:
# Do not allow 0-d arrays because following code fails for scalar
zerod = True
q = q[None]
else:
zerod = False

q = q / 100.0
if (q < 0).any() or (q > 1).any():
raise ValueError(
"Percentiles must be in the range [0,100]")
# avoid expensive reductions, relevant for arrays with < O(1000) elements
if q.size < 10:
for i in range(q.size):
if q[i] < 0. or q[i] > 100.:
raise ValueError("Percentiles must be in the range [0,100]")
q[i] /= 100.
else:
# faster than any()
if np.count_nonzero(q < 0.) or np.count_nonzero(q > 100.):
raise ValueError("Percentiles must be in the range [0,100]")
q /= 100.

# prepare a for partioning
if overwrite_input:
Expand Down
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