[Numpy-discussion] boolean masks & lists

John Hunter jdh2358@gmail....
Mon Nov 5 14:57:11 CST 2007


A colleague of mine just asked for help with a pesky bug that turned
out to be caused by his use of a list of booleans rather than an array
of booleans as his logical indexing mask.  I assume this is a feature
and not a bug, but it certainly surprised him:

In [58]: mask = [True, False, False, False, True]

In [59]: maska = n.array(mask, n.bool)

In [60]: x = arange(5)

In [61]: x[mask]
Out[61]: array([1, 0, 0, 0, 1])

In [62]: x[maska]
Out[62]: array([0, 4])


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