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
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]
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