[Numpy-discussion] finding elements that match any in a set

[Skipper Seabold]

On Fri, May 27, 2011 at 12:48 PM, Michael Katz
<michaeladamkatz at yahoo.com> wrote:
> I have a numpy array, records, with named fields including a field named
> "integer_field". I have an array (or list) of values of interest, and I want
> to get the indexes where integer_field has any of those values.
>
> Because I can do
>
>     indexes = np.where( records.integer_field > 5 )
>
> I thought I could do
>
>     indexes = np.where( records.integer_field in values )
>
> But that doesn't work. (As a side question I'm interested in why that
> doesn't work, when values is a python list.)
>
> How can I get those indexes? I though perhaps I need a nested np.where, or
> some other two-step process, but it wasn't clear to me how to do it.
>

Check out this recent thread. I think the proposed class does what you
want. It's more efficient than in1d, if values is small compared to
the length of records.

http://thread.gmane.org/gmane.comp.python.scientific.user/29035/

Skipper