Keith Goodman <kwgoodman <at> gmail.com> writes:

On Tue, Dec 9, 2008 at 12:25 PM, Bab Tei <babaktei <at> yahoo.com> wrote:

...

I can exclude a list of items by using negative index in R (R-project) ie

myarray[-excludeindex]. As

negative indexing in numpy (And python) behave differently ,how can I exclude a list of item in numpy?

Here's a painful way to do it:

...

...

x = np.array([0,1,2,3,4]) excludeindex = [1,3] idx = list(set(range(4)) - set(excludeindex)) x[idx] array([0, 2])

To make it more painful, you might want to sort idx.

But if excludeindex is True/False, then just use ~excludeindex.

Thank you. However it seems I have to create a full list at first and then exclude items. It is somehow painful as I have some very large sparse matrices and creating a full index eats a lot of memory. Maybe adding this functionality to numpy saves memory and makes the syntax more clear ie a syntax like x[~excludeindex] which smartly distinguish between excludeindex as a list of numerical indexes and a mask (list of true/false indexes). Regards