[Numpy-discussion] Selecting columns of a matrix (original) (raw)

Pau Gargallo pau.gargallo at gmail.com
Wed Jun 21 13:09:50 EDT 2006

On 6/21/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:

Johannes Loehnert wrote: > Hi, > > >> I'm not sure why bool arrays cannot be used as indices. >> The "natural" solution to the original problem seemed to be: >> M[:,V>0] >> but this is not allowed. >> > > I started a thread on this earlier this year. Try searching the archive for > "boolean indexing" (if it comes back online somewhen). > > Travis had some reason for not implementing this, but unfortunately I do not > remember what it was. The corresponding message might still linger on my home > > PC, which I can access this evening.... >

I suspect my reason was just not being sure if it could be explained consistently. But, after seeing this come up again. I decided it was easy enough to implement. So, in SVN NumPy, you will be able to do a[:,V>0] a[V>0,:] The V>0 will be replaced with integer arrays as if nonzero(V>0) had been called.

does it work for a[,] ?

what about a[ix_( nonzero(), nonzero() )] ?

maybe the to nonzero() conversion would be more coherently done by the ix_ function than by the []

pau

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