On Wednesday, March 7, 2012, Neal Becker <ndbeck...@gmail.com> wrote: > Charles R Harris wrote: > >> On Wed, Mar 7, 2012 at 1:05 PM, Neal Becker <ndbeck...@gmail.com> wrote: >> >>> I'm wondering what is the use for the ignored data feature? >>> >>> I can use: >>> >>> A[valid_A_indexes] = whatever >>> >>> to process only the 'non-ignored' portions of A. So at least some simple >>> cases >>> of ignored data are already supported without introducing a new type. >>> >>> OTOH: >>> >>> w = A[valid_A_indexes] >>> >>> will copy A's data, and subsequent use of >>> >>> w[:] = something >>> >>> will not update A. >>> >>> Is this the reason for wanting the ignored data feature? >>> >> >> Suppose you are working with plotted data and want to turn points on/off by >> clicking on them interactively to see how that affects a fit. Why make >> multiple copies, change sizes, destroy data, and all that nonsense? Just >> have the click update the mask and redraw. >> >> Chuck > > But does > > some_func (A[valid_data_mask]) > > actually perform a copy? > >
Yes! If it isn't sliced, or accessed by a scalar index, then you are given a copy. Fancy indexing and Boolean indexing will not return a view. Note that assignments to a Boolean-indexed array by a scalar is special-cased. I.e., A[valid_points] = 5 will do what you expect. But, A[valid_points] += 5 may not, IIRC. Ben Root
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