On Wed, Jan 10, 2007 at 08:28:14PM +0100, Francesc Altet wrote: > El dt 09 de 01 del 2007 a les 23:19 +0900, en/na David Cournapeau va > escriure: > > Hi, > > > > I am finally implementing a C function to replace the current slow > > implementation of clip in python as promised a few weeks ago. The idea > > is to implement it as the following: > > > > def clip(input, min, max): > > a = input.copy() > > putmask(a, a <= min, min) > > putmask(a, a >= max, max) > > return a > > > > I don't have that much experience in writing general numpy functions, so > > I was wondering of other people could advise me on the following points. > > > > Sorry, but not real experience writing extensions directly in C. > However, you may want to experiment using numexpr for doing what you > want. It's relatively easy to extend numexpr and adding a new opcode to > its virtual machine. I'm attaching a patch for implementing such a clip > routine (only for floating point types, but given the example, it should > be straightforward to add support for integers as well). > > Also, you should note that using the fancy indexing of numpy seems to > perform better than the putmask approach. Below are my figures for a > small benchmark (also attached) for testing the performance of clip > using several approaches: > > time (putmask)--> 1.38 > time (where)--> 2.713 > time (numexpr where)--> 1.291 > time (fancy+assign)--> 0.967 > time (numexpr clip)--> 0.596 > > It is interesting to see there how fancy-indexing + assignation is quite > more efficient than putmask.
Not on my machine: time (putmask)--> 0.181 time (where)--> 0.783 time (numexpr where)--> 0.26 time (fancy+assign)--> 0.202 Cheers Stéfan _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
