Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Nicolas P. Rougier
On 22 Jun 2014, at 22:52, Eelco Hoogendoorn wrote: > That's pretty cool; and it makes sense that way. Still, couldn't you fold > this kind of computation into a shader? > > Have you looked at vispy btw? I think its a really nice initiative; having a > high quality vector graphics module in th

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Eelco Hoogendoorn
That's pretty cool; and it makes sense that way. Still, couldn't you fold this kind of computation into a shader? Have you looked at vispy btw? I think its a really nice initiative; having a high quality vector graphics module in there would make it even better. Would be nice if those projects cou

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Nicolas P. Rougier
Actually, it's already working pretty well but it slows down when you're doing a lot of zoom in/out. The trick is that rendering is done using shader (OpenGL) and this computation is used to give information to the shader to where to draw antialiased lines. In the end, this shader is able to d

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Eelco Hoogendoorn
Protip: if you are writing your own rasterization code in python, be prepared to forget about performance altogether. Something like numba or other c-like extension will be necessary unless you are willing to leave big gobs of performance on the table; and even with pure C you will get nowhere clo

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Nicolas P. Rougier
Thanks, I'll try your solution. Data (L) is not so big actually, it represents pixels on screen and (I) represents line position (for grids). I need to compute this quantity everytime the user zoom in or out. Nicolas On 22 Jun 2014, at 19:05, Eelco Hoogendoorn wrote: > Well, if the spacin

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Eelco Hoogendoorn
Also, if you use scipy.spatial.KDTree, make sure to use cKDTree; the native python kdtree is sure to be slow as hell. On Sun, Jun 22, 2014 at 7:05 PM, Eelco Hoogendoorn < hoogendoorn.ee...@gmail.com> wrote: > Well, if the spacing is truly uniform, then of course you don't really > need the searc

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Eelco Hoogendoorn
Well, if the spacing is truly uniform, then of course you don't really need the search, and you can do away with the extra log-n, and there is a purely linear solution: def find_closest_direct(start, end, count, A): Q = (A-start)/(end-start)*count mid = ((Q[1:]+Q[:-1]+1)/2).astype(np.int)

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Benjamin Root
I would echo KDTree, but one way I think you can simplify the existing code you have is to shift the values of L by half the spacing, then you shouldn't need the check for left and right values. Cheers! Ben Root On Sun, Jun 22, 2014 at 4:22 AM, Nicolas P. Rougier < nicolas.roug...@inria.fr> wrot

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Sebastian Berg
On So, 2014-06-22 at 17:16 +0200, Nicolas P. Rougier wrote: > Thanks for the answer. > I was secretly hoping for some kind of hardly-known numpy function that would > make things faster auto-magically... > I doubt it is faster, but if you got scipy anyway, using KDTree may be pretty idiomatic.

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Nicolas P. Rougier
Thanks for the answer. I was secretly hoping for some kind of hardly-known numpy function that would make things faster auto-magically... Nicolas On 22 Jun 2014, at 10:30, Eelco Hoogendoorn wrote: > Perhaps you could simplify some statements, but at least the algorithmic > complexity is f

Re: [Numpy-discussion] Find n closest values

2014-06-22 Thread Eelco Hoogendoorn
Perhaps you could simplify some statements, but at least the algorithmic complexity is fine, and everything is vectorized, so I doubt you will get huge gains. You could take a look at the functions in scipy.spatial, and see how they perform for your problem parameters. On Sun, Jun 22, 2014 at 10

[Numpy-discussion] Find n closest values

2014-06-22 Thread Nicolas P. Rougier
Hi, I have an array L with regular spaced values between 0 and width. I have a (sorted) array I with irregular spaced values between 0 and width. I would like to find the closest value in I for any value in L. Currently, I'm using the following script but I wonder if I missed an obvious (and