Comparing boolean numpy arrays

Question

I have two boolean numpy arrays of similar shape like:

a=[[True,True,False,False]]
b=[[True,False,True,False]]

How can I get an array c where 1 indicates that only array a is true, 2 indicates that only array b is true, 0 where both arrays are false and nan where both are true. So in this case the result should be [[nan,1,2,0]]].

I've updated the question: if both are true an 'nan' should be returned — Johannes
– Johannes, Commented Dec 7, 2015 at 11:33

unutbu · Accepted Answer · 2015-12-07 11:36:56Z

4

You could use np.select:

In [20]: a = np.array([True,True,False,False])

In [21]: b = np.array([True,False,True,False])

In [23]: np.select([a&~b, b&~a, a&b], [1, 2, np.nan], default=0)
Out[23]: array([ nan,   1.,   2.,   0.])

answered Dec 7, 2015 at 11:36

unutbu

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Divakar · Accepted Answer · 2015-12-07 11:41:37Z

4

You could use np.where -

np.where(a*b,np.nan,(2*b + a))

Sample run -

In [60]: a
Out[60]: array([[ True,  True, False, False]], dtype=bool)

In [61]: b
Out[61]: array([[ True, False,  True, False]], dtype=bool)

In [62]: np.where(a*b,np.nan,(2*b + a))
Out[62]: array([[ nan,   1.,   2.,   0.]])

edited Dec 7, 2015 at 11:41

answered Dec 7, 2015 at 11:35

Divakar

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