Question

I have two numpy arrays: a and b. I want to select all of the indices where a == 1 and b == 0.

That is, if I have the following arrays:

a = [0, 1, 3, 5, 1, 1, 2]

b = [1, 0, 2, 5, 3, 0, 6]

I would like to get the following indices back:

[1, 5]

How should I do this in numpy? I have tried using the following (suggested by a quick reference guide showing differences between numpy, matlab and IDL):

(a == 1 and b == 0).nonzero()

But that gives an error about truth values being ambiguous.

Any ideas?

Answer 1

In []: from numpy import array, logical_and
In []: a= array([0, 1, 3, 5, 1, 1, 2])
In []: b= array([1, 0, 2, 5, 3, 0, 6])
In []: logical_and(a== 1, b== 0).nonzero()[0]
Out[]: array([1, 5])

Obviously this will work as well:

In []: ((a== 1)& (b== 0)).nonzero()[0]
Out[]: array([1, 5])