[Numpy-discussion] indexing bug in numpy r2694 (original) (raw)

Keith Goodman kwgoodman at gmail.com
Wed Jun 28 15:23:36 EDT 2006

On 6/28/06, Travis Oliphant <oliphant at ee.byu.edu> wrote:

Keith Goodman wrote:

>On 6/28/06, Pau Gargallo <pau.gargallo at gmail.com> wrote: > > >>i don't know why 'where' is returning matrices. >>if you use: >> >> >> >>>>>idx = where(y.A > 0.5)[0] >>>>> >>>>> >>everything will work fine (I guess) >> >> > >What about the second issue? Is this expected behavior? > > > >>>idx >>> >>> >array([0, 1, 2]) > > > >>>y >>> >>> > >matrix([[ 0.63731308], > [ 0.34282663], > [ 0.53366791]]) > > > >>>y[idx] >>> >>> > >matrix([[ 0.63731308], > [ 0.34282663], > [ 0.53366791]]) > > > >>>y[idx,0] >>> >>> >matrix([[ 0.63731308, 0.34282663, 0.53366791]]) > >I was expecting a column vector. > > > This should be better behaved now in SVN. Thanks for the reports.

Now numpy can do

y[y > 0.5]

instead of

y[where(y.A > 0.5)[0]]

where, for example, y = asmatrix(rand(3,1)).

I know I'm pushing my luck here. But one more feature would make this perfect.

Currently y[y>0.5,:] returns the first column even if y has more than one column. Returning all columns would make it perfect.

Example:

y

matrix([[ 0.38828902, 0.91649964], [ 0.41074001, 0.7105919 ], [ 0.15460833, 0.16746956]])

y[y[:,1]>0.5,:]

matrix([[ 0.38828902], [ 0.41074001]])

A better answer for matrix users would be:

y[(0,1),:]

matrix([[ 0.38828902, 0.91649964], [ 0.41074001, 0.7105919 ]])

More information about the NumPy-Discussion mailing list