Thread Subject: creating a sparse matrix from a file

i have a list in following form (in a csv file)
12,54
3,4
.
.
.
i trying to create a sparse matrix by using following code

smat(12,54)=1;

now the size of the list is around 1 million that is there are around
1million pairs.
a simple for loop is taking 30 minutes for 10 percent of of values.
is there any shortcut way for this.
to speed up the process?

akshay bhat <akshayubhat@gmail.com> wrote in message
<2b89e1a3-a4f7-47ae-b8e0-571a8aa640d1@h1g2000prh.googlegroups.com>...
> i have a list in following form (in a csv file)
> 12,54
> 3,4
> .
> .
> .
> i trying to create a sparse matrix by using following code
>
> smat(12,54)=1;
>
> now the size of the list is around 1 million that is there
are around
> 1million pairs.
> a simple for loop is taking 30 minutes for 10 percent of
of values.
> is there any shortcut way for this.
> to speed up the process?

Save the file in space or tab-delimited form, without the
commas. Then do

load smat.txt
A = sparse(smat(:,1),smat(:,2),1) ;

The code is slow because you are abusing subsref (the
smat(i,j)=1 statement).

If you can't remove the commas, do:

f=fopen('smat.csv') ;
t = fscanf (f,'%d, %d') ;
fclose(f) ;
t = reshape (t, 2, length(t)/2)' ;
A = sparse (t(:,1), t(:,2), 1) ;

See Loren's March 1st, 2007 blog for more details.

Astute readers might know of something better than the
reshape I'm using.

On May 5, 1:33 am, "Tim Davis" <da...@cise.ufl.edu> wrote:
> akshay bhat <akshayub...@gmail.com> wrote in message
>
> <2b89e1a3-a4f7-47ae-b8e0-571a8aa64...@h1g2000prh.googlegroups.com>...
>
>
>
> > i have a list in following form (in a csv file)
> > 12,54
> > 3,4
> > .
> > .
> > .
> > i trying to create a sparse matrix by using following code
>
> > smat(12,54)=1;
>
> > now the size of the list is around 1 million that is there
> are around
> > 1million pairs.
> > a simple for loop is taking 30 minutes for 10 percent of
> of values.
> > is there any shortcut way for this.
> > to speed up the process?
>
> Save the file in space or tab-delimited form, without the
> commas. Then do
>
> load smat.txt
> A = sparse(smat(:,1),smat(:,2),1) ;
>
> The code is slow because you are abusing subsref (the
> smat(i,j)=1 statement).
>
> If you can't remove the commas, do:
>
> f=fopen('smat.csv') ;
> t = fscanf (f,'%d, %d') ;
> fclose(f) ;
> t = reshape (t, 2, length(t)/2)' ;
> A = sparse (t(:,1), t(:,2), 1) ;
>
> See Loren's March 1st, 2007 blog for more details.
>
> Astute readers might know of something better than the
> reshape I'm using.

hey thanks a lot for help

akshay bhat:
<SNIP sparse mat from a list of indices...

> i have a list in following form (in a csv file)
> 12,54
> 3,4
> i trying to create a sparse matrix by using following code
> smat(12,54)=1;

a hint:

     help spconvert;

us