[Numpy-discussion] using boolean arrays as indices

Michael Sorich michael.sorich at gmail.com
Mon Mar 27 16:31:03 CST 2006

If I have a 2D array and I want to use a boolean array to select the rows.
If I use a[boolarray] it works, but if I use a[boolarray, :] an exception is
raised. Is there a reason for this?

>>>a = N.arange(10).reshape((2,5))
array([[0, 1, 2, 3, 4],
       [5, 6, 7, 8, 9]])
>>>a[N.array([True, False])]
array([[0, 1, 2, 3, 4]])
>>>a[N.array([True, False]),:]
Traceback (most recent call last):
  File "<input>", line 1, in ?
IndexError: arrays used as indices must be of integer type
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