[Numpy-discussion] suggestions for Matrix-related changes

Michael Sorich michael.sorich at gmail.com
Tue Jul 11 19:07:56 CDT 2006


On 7/12/06, JJ <josh8912 at yahoo.com> wrote:

> 2) It would be very convienient to have some simple way to delete selected
> columns of a matrix.  For example, in matlab the command is X[:,[3,5,7]]=[] to
> delete the three selected columns.  It would be nice if such a command would
> also work with selections, as in X[:,A[0,:]<4] = [], where X and A are matrices.

+1.
In R negative integers are used for this purpose and a copy of the
array is returned. e.g.
> x = 1:10
> x
 [1]  1  2  3  4  5  6  7  8  9 10
> x[-1]
[1]  2  3  4  5  6  7  8  9 10
> x[c(-1,-2)]
[1]  3  4  5  6  7  8  9 10
> x[-c(1,2)]
[1]  3  4  5  6  7  8  9 10

I like the current use of negative indices in numpy, but I do find
myself missing the ability to easily make a copy of the array without
certain indices.

Mike




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