[Numpy-discussion] Masking an array with another array

Gael Varoquaux gael.varoquaux@normalesup....
Thu Apr 23 00:16:15 CDT 2009


On Wed, Apr 22, 2009 at 04:21:05PM -0500, Gökhan SEVER wrote:
>    Could you please give me some hints about how to mask an array using
>    another arrays like in the following example.

>    In [14]: a = arange(5)

>    In [15]: a
>    Out[15]: array([0, 1, 2, 3, 4])

>    and my secondary array is "b"

>    In [16]: b = array([2,3])

>    What I want to do is to mask a with b values and get an array of:

>    array([False, False, True, True,  False], dtype=bool)

This is an operation on 'sets': you are testing if members of a are 'in'
b. Generally, set operations on arrays can be found in
numpy.lib.arraysetops. I believe what you are interested in is
setmember1d.

HTH,

Gaël


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