Re: [Numpy-discussion] list to array is slow

On Thu, Jul 22, 2010 at 5:09 PM, marco cammarata <marcocamma@gmail.com> wrote:

Hi,

any idea why the simple code below is so slow ?

import numpy as n from time import time as t

dims = (640,480) m = n.random.random( dims )

l=[]

for i in range(200):        l.append(m)

t0=t() b=n.array(l) print t()-t0

To convert the list into an array takes about 5 sec ...

There was a recent thread that covers similar ground. "Stacking arrays along new dimension in front" http://www.mail-archive.com/numpy-discussion@scipy.org/msg26772.html I think the fastest way was to do b = n.concatenate(a_[None] for a_ in l) but I could be mistaken, and there should probably be a more general solution to this problem. Skipper