Re: [Numpy-discussion] Most efficient trim of arrays

On Tue, Dec 14, 2010 at 12:20, Mark Janikas wrote:

Hello All,

I was wondering what the best way to trim an array based on some values I do not want….  I could use NUM.where or NUM.take… but let me give you an example:

import numpy as NUM

n = 100 (Length of my dataset) data = NUM.empty((n,), float) badRecords = [] for ind, record in enumerate(records):                 if record == someValueIDOntWant:                                 badRecords.append(ind)                 else:                                 data[ind] = record

Now, I want to “trim” my array using badRecords.  I guess I want to avoid copying.  Any thoughts on the best way to do it?  I do not want to use lists and then subsequently array the result as it is nice to pre-allocate the space.

Don't fear the copy. Use boolean indexing. http://docs.scipy.org/doc/numpy/reference/arrays.indexing.html#boolean -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth."   -- Umberto Eco