Multiple logical index select numpy array

Question

Well, if we want to choose certain values to remain the same, and set others values to zero in a numpy array, we can

A = A == 1

if A has only 4 unique numbers 0,1,2,3.

However, if I want to select N different values, like

A = np.where(A==1 or A==2, A)

but this does not work, and the conditions are not neccessarily for 2 values only. How can i implement this idea?

Djaouad · Accepted Answer · 2019-09-09 23:04:17Z

1

Just a note when using multiple conditions, use the bitwise OR operator (|) and enclose each condition in parenthesis:

A = np.where((A == 1) | (A == 2), A, 0)

And for this task, you can use numpy.isin:

A = np.where(numpy.isin(A, [1, 2]), A, 0)

answered Sep 9, 2019 at 22:49

Djaouad

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