numpy.extract

numpy.extract(condition, arr)[source]

Return the elements of an array that satisfy some condition.

This is equivalent to np.compress(ravel(condition), ravel(arr)). If condition is boolean np.extract is equivalent to arr[condition].

Note that place does the exact opposite of extract.

Parameters:

conditionarray_like

An array whose nonzero or True entries indicate the elements of arr to extract.

arrarray_like

Input array of the same size as condition.

Returns:

extractndarray

Rank 1 array of values from arr where condition is True.

See also

take, put, copyto, compress, place

Examples

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>>> import numpy as np
>>> arr = np.arange(12).reshape((3, 4))
>>> arr
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])
>>> condition = np.mod(arr, 3)==0
>>> condition
array([[ True, False, False,  True],
       [False, False,  True, False],
       [False,  True, False, False]])
>>> np.extract(condition, arr)
array([0, 3, 6, 9])

If condition is boolean:

>>> arr[condition]
array([0, 3, 6, 9])

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