[Numpy-discussion] puzzle: generate index with many ranges
Fri Jan 30 13:06:26 CST 2009
On Jan 30, 2009, at 1:53 PM, Raik Gruenberg wrote:
> Pierre GM wrote:
>> On Jan 30, 2009, at 1:11 PM, Raik Gruenberg wrote:
>>> Mhm, I got this far. But how do I get from here to a single index
>>> [ 4, 5, 6, ... 10, 0, 1, 2, 3, 11, 12, 13, 14 ] ?
>> np.concatenate([np.arange(aa,bb) for (aa,bb) in zip(a,b)])
> exactly! Now, the question was, is there a way to do this only using
> functions (sum, repeat, ...), that means without any python "for"
Can't really see it right now. Make np.arange(max(b)) and take the
slices you need ? But you still have to look in 2 arrays to find the
beginning and end of slices, so...
> Sorry about being so insistent on this one but, in my experience,
> those for loops makes a huge difference in terms of speed. The zip
> is probably
> also quite costly on a very large data set.
yeah, but it's in a list comprehension, which may make things a tad
faster. If you prefer, use itertools.izip instead of zip, but I wonder
where the advantage would be. Anyway, are you sure this particular
part is your bottleneck ? You know the saying about premature
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