bottleneck.nonreduce_axis module

Module contents

Bottleneck non-reducing functions that operate along an axis.

bottleneck.nonreduce_axis.argpartition(a, kth, axis=-1)

Return indices that would partition array along the given axis.

A 1d array B is partitioned at array index kth if three conditions are met: (1) B[kth] is in its sorted position, (2) all elements to the left of kth are less than or equal to B[kth], and (3) all elements to the right of kth are greater than or equal to B[kth]. Note that the array elements in conditions (2) and (3) are in general unordered.

Shuffling the input array may change the output. The only guarantee is given by the three conditions above.

This functions is not protected against NaN. Therefore, you may get unexpected results if the input contains NaN.

Parameters

aarray_like

Input array. If a is not an array, a conversion is attempted.

kthint

The value of the element at index kth will be in its sorted position. Smaller (larger) or equal values will be to the left (right) of index kth.

axis{int, None}, optional

Axis along which the partition is performed. The default (axis=-1) is to partition along the last axis.

Returns

yndarray

An array the same shape as the input array containing the indices that partition a. The dtype of the indices is numpy.intp.

See also

bottleneck.partition

Partition array elements along given axis.

Notes

Unexpected results may occur if the input array contains NaN.

Examples

Create a numpy array:

>>> a = np.array([10, 0, 30, 40, 20])

Find the indices that partition the array so that the first 3 elements are the smallest 3 elements:

>>> index = bn.argpartition(a, kth=2)
>>> index
array([0, 1, 4, 3, 2])

Let’s use the indices to partition the array (note, as in this example, that the smallest 3 elements may not be in order):

>>> a[index]
array([10, 0, 20, 40, 30])

bottleneck.nonreduce_axis.nanrankdata(a, axis=None)

Ranks the data, dealing with ties and NaNs appropriately.

Equal values are assigned a rank that is the average of the ranks that would have been otherwise assigned to all of the values within that set. Ranks begin at 1, not 0.

NaNs in the input array are returned as NaNs.

Parameters

aarray_like

Input array. If a is not an array, a conversion is attempted.

axis{int, None}, optional

Axis along which the elements of the array are ranked. The default (axis=None) is to rank the elements of the flattened array.

Returns

yndarray

An array with the same shape as a. The dtype is ‘float64’.

See also

bottleneck.rankdata

Ranks the data, dealing with ties and appropriately.

Examples

>>> bn.nanrankdata([np.nan, 2, 2, 3])
array([ nan,  1.5,  1.5,  3. ])
>>> bn.nanrankdata([[np.nan, 2], [2, 3]])
array([ nan,  1.5,  1.5,  3. ])
>>> bn.nanrankdata([[np.nan, 2], [2, 3]], axis=0)
array([[ nan,   1.],
       [  1.,   2.]])
>>> bn.nanrankdata([[np.nan, 2], [2, 3]], axis=1)
array([[ nan,   1.],
       [  1.,   2.]])

bottleneck.nonreduce_axis.partition(a, kth, axis=-1)

Partition array elements along given axis.

A 1d array B is partitioned at array index kth if three conditions are met: (1) B[kth] is in its sorted position, (2) all elements to the left of kth are less than or equal to B[kth], and (3) all elements to the right of kth are greater than or equal to B[kth]. Note that the array elements in conditions (2) and (3) are in general unordered.

Shuffling the input array may change the output. The only guarantee is given by the three conditions above.

This functions is not protected against NaN. Therefore, you may get unexpected results if the input contains NaN.

Parameters

aarray_like

Input array. If a is not an array, a conversion is attempted.

kthint

The value of the element at index kth will be in its sorted position. Smaller (larger) or equal values will be to the left (right) of index kth.

axis{int, None}, optional

Axis along which the partition is performed. The default (axis=-1) is to partition along the last axis.

Returns

yndarray

A partitioned copy of the input array with the same shape and type of a.

See also

bottleneck.argpartition

Indices that would partition an array

Notes

Unexpected results may occur if the input array contains NaN.

Examples

Create a numpy array:

>>> a = np.array([1, 0, 3, 4, 2])

Partition array so that the first 3 elements (indices 0, 1, 2) are the smallest 3 elements (note, as in this example, that the smallest 3 elements may not be sorted):

>>> bn.partition(a, kth=2)
array([1, 0, 2, 4, 3])

Now Partition array so that the last 2 elements are the largest 2 elements:

>>> bn.partition(a, kth=3)
array([1, 0, 2, 3, 4])

bottleneck.nonreduce_axis.push(a, n=None, axis=-1)

Fill missing values (NaNs) with most recent non-missing values.

Filling proceeds along the specified axis from small index values to large index values.

Parameters

aarray_like

Input array. If a is not an array, a conversion is attempted.

n{int, None}, optional

How far to push values. If the most recent non-NaN array element is more than n index positions away, than a NaN is returned. The default (n = None) is to push the entire length of the slice. If n is an integer it must be nonnegative.

axisint, optional

Axis along which the elements of the array are pushed. The default (axis=-1) is to push along the last axis of the input array.

Returns

yndarray

An array with the same shape and dtype as a.

See also

bottleneck.replace

Replace specified value of an array with new value.

Examples

>>> a = np.array([5, np.nan, np.nan, 6, np.nan])
>>> bn.push(a)
    array([ 5.,  5.,  5.,  6.,  6.])
>>> bn.push(a, n=1)
    array([  5.,   5.,  nan,   6.,   6.])
>>> bn.push(a, n=2)
    array([ 5.,  5.,  5.,  6.,  6.])

bottleneck.nonreduce_axis.rankdata(a, axis=None)

Ranks the data, dealing with ties appropriately.

Equal values are assigned a rank that is the average of the ranks that would have been otherwise assigned to all of the values within that set. Ranks begin at 1, not 0.

Parameters

aarray_like

Input array. If a is not an array, a conversion is attempted.

axis{int, None}, optional

Axis along which the elements of the array are ranked. The default (axis=None) is to rank the elements of the flattened array.

Returns

yndarray

An array with the same shape as a. The dtype is ‘float64’.

See also

bottleneck.nanrankdata

Ranks the data dealing with ties and NaNs.

Examples

>>> bn.rankdata([0, 2, 2, 3])
array([ 1. ,  2.5,  2.5,  4. ])
>>> bn.rankdata([[0, 2], [2, 3]])
array([ 1. ,  2.5,  2.5,  4. ])
>>> bn.rankdata([[0, 2], [2, 3]], axis=0)
array([[ 1.,  1.],
       [ 2.,  2.]])
>>> bn.rankdata([[0, 2], [2, 3]], axis=1)
array([[ 1.,  2.],
       [ 1.,  2.]])