[Numpy-discussion] another little index puzzle

[Robert Kern]

On Mon, Jan 21, 2013 at 2:41 PM, Neal Becker <ndbecker2 at gmail.com> wrote:
> I have an array to be used for indexing.  It is 2d, where the rows are all the
> permutations of some numbers.  So:
>
> array([[-2, -2, -2],
>        [-2, -2, -1],
>        [-2, -2,  0],
>        [-2, -2,  1],
>        [-2, -2,  2],
>  ...
>        [ 2,  1,  2],
>        [ 2,  2, -2],
>        [ 2,  2, -1],
>        [ 2,  2,  0],
>        [ 2,  2,  1],
>        [ 2,  2,  2]])
>
> Here the array is 125x3
>
> I want to select all the rows of the array in which all the 3 elements are
> equal, so I can remove them.  So for example, the 1st and last row.

all_equal_mask = np.logical_and.reduce(arr[:,1:] == arr[:,:-1], axis=1)
some_unequal = arr[~all_equal_mask]

--
Robert Kern