How to create a numpy array of all True or all False?

python arrays numpy boolean numpy-ndarray
Michael Currie picture Michael Currie · Jan 17, 2014 · Viewed 224.3k times · Source

In Python, how do I create a numpy array of arbitrary shape filled with all True or all False?

Answer

Michael Currie picture Michael Currie · Jan 17, 2014

numpy already allows the creation of arrays of all ones or all zeros very easily:

e.g. numpy.ones((2, 2)) or numpy.zeros((2, 2))

Since True and False are represented in Python as 1 and 0, respectively, we have only to specify this array should be boolean using the optional dtype parameter and we are done.

numpy.ones((2, 2), dtype=bool)

returns:

array([[ True,  True],
       [ True,  True]], dtype=bool)

UPDATE: 30 October 2013

Since numpy version 1.8, we can use full to achieve the same result with syntax that more clearly shows our intent (as fmonegaglia points out):

numpy.full((2, 2), True, dtype=bool)

UPDATE: 16 January 2017

Since at least numpy version 1.12, full automatically casts results to the dtype of the second parameter, so we can just write:

numpy.full((2, 2), True)

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