How do I convert a numpy matrix into a boolean matrix?

Question

I have a n x n matrix in numpy which has 0 and non-0 values. Is there a way to easily convert it to a boolean matrix?

Thanks.

Do the zero values need to be set to false? Or is there another condition? — nicholaschris
– nicholaschris, Commented Dec 4, 2013 at 10:44

user2357112 · Accepted Answer · 2013-12-04 10:58:56Z

48

numpy.array(old_matrix, dtype=bool)

Alternatively,

old_matrix != 0

The first version is an elementwise coercion to boolean. Analogous constructs will work for conversion to other data types. The second version is an elementwise comparison to 0. It involves less typing, but ran slightly slower when I timed it. Which you use is up to you; I'd probably decide based on whether "convert to boolean" or "compare to 0" is a better conceptual description of what I'm after.

edited Dec 4, 2013 at 10:58

answered Dec 4, 2013 at 10:52

user2357112

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seberg · Accepted Answer · 2013-12-04 12:37:31Z

22

You should use array.astype(bool) (or array.astype(dtype=bool)). Works with matrices too.

answered Dec 4, 2013 at 12:37

seberg

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Ray · Accepted Answer · 2013-12-04 10:50:09Z

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Simply use equality check:

Suppose a is your numpy matrix, use b = (a == 0) or b = (a != 0) to get the boolean value matrix.

In some case, since the value maybe sufficiently small but non-zero, you may use abs(a) < TH, where TH is the numerical threshold you set.

answered Dec 4, 2013 at 10:50

Ray

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Community · Accepted Answer · 2020-06-20 09:12:55Z

5

.astype(dtype)

https://docs.scipy.org/doc/numpy-1.13.0/reference/generated/numpy.ndarray.astype.html

It's nice that this will work on binary-like floats including 0. and 1..

old_matrix.astype(bool)

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 5, 2019 at 2:57

LayneSadler

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