numpy.intersect1d#

numpy.intersect1d(ar1, ar2, assume_unique=False, return_indices=False)[source]#

Find the intersection of two arrays.

Return the sorted, unique values that are in both of the input arrays.

Parameters:

ar1, ar2array_like: Input arrays. Will be flattened if not already 1D.
assume_uniquebool: If True, the input arrays are both assumed to be unique, which can speed up the calculation. If True but ar1 or ar2 are not unique, incorrect results and out-of-bounds indices could result. Default is False.
return_indicesbool: If True, the indices which correspond to the intersection of the two arrays are returned. The first instance of a value is used if there are multiple. Default is False.

Returns:

intersect1dndarray: Sorted 1D array of common and unique elements.
comm1ndarray: The indices of the first occurrences of the common values in ar1. Only provided if return_indices is True.
comm2ndarray: The indices of the first occurrences of the common values in ar2. Only provided if return_indices is True.

Examples

>>> import numpy as np
>>> np.intersect1d([1, 3, 4, 3], [3, 1, 2, 1])
array([1, 3])

To intersect more than two arrays, use functools.reduce:

>>> from functools import reduce
>>> reduce(np.intersect1d, ([1, 3, 4, 3], [3, 1, 2, 1], [6, 3, 4, 2]))
array([3])

To return the indices of the values common to the input arrays along with the intersected values:

>>> x = np.array([1, 1, 2, 3, 4])
>>> y = np.array([2, 1, 4, 6])
>>> xy, x_ind, y_ind = np.intersect1d(x, y, return_indices=True)
>>> x_ind, y_ind
(array([0, 2, 4]), array([1, 0, 2]))
>>> xy, x[x_ind], y[y_ind]
(array([1, 2, 4]), array([1, 2, 4]), array([1, 2, 4]))