# Returning the positions of a list that are non-zero

Chris cwitts at gmail.com
Wed Jul 9 15:29:09 CEST 2008

```On Jul 9, 7:48 am, "Rajanikanth Jammalamadaka" <rajanika... at gmail.com>
wrote:
> Try this:
>
> >>> li=[0,0,1,2,1,0,0]
> >>> li
>
> [0, 0, 1, 2, 1, 0, 0]>>> [i for i in range(len(li)) if li[i] != 0]
>
> [2, 3, 4]
>
> Cheers,
>
> Raj
>
>
>
> On Tue, Jul 8, 2008 at 10:26 PM, Benjamin Goudey <bwgou... at gmail.com> wrote:
> > I have a very large list of integers representing data needed for a
> > histogram that I'm going to plot using pylab. However, most of these
> > values (85%-95%) are zero and I would like to remove them to reduce
> > the amount of memory I'm using and save time when it comes to plotting
> > the data. To do this, I'm trying to find the best way to remove all of
> > the zero values and produce a list of indices of where the non-zero
> > values used to be.
>
> > For example, if my original list is [0,0,1,2,1,0,0] I would like to
> > produce the lists [1,2,1] (the non zero values) and [2,3,4] (indices
> > of where the non-zero values used to be). Removing non-zero values is
> > very easy but determining the indicies is where I'm having difficulty.
>
> > Thanks in advance for any help
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
> --
> "For him who has conquered the mind, the mind is the best of friends;
> but for one who has failed to do so, his very mind will be the
> greatest enemy."
>
> Rajanikanth

That's a waste

>>> li=[0,0,1,2,1,0,0]
>>> [i for i in li if i]

That's all you need. :)

```