extracting a random subset of a vector

Hi all, I have an optimization problem.

I currently use the following code to select a random subset of a rank-1 
array:

----------------------------------------------------------

import numarray as NA
import numarray.random_array as RA

N = 1000
M = 100
full = NA.arange(N)
subset = full[RA.permutation(N)][:M]

---------------------------------------------------------

However, it's quite slow (at least with N~40k), and from the hotshot 
output is looks like it's the indexing, not the permutation, which takes 
time.
Does anyone have a suggestion on a faster pure-python implementation?

thanks


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