Re: How do I replace this for-loop?

[Francesco Potorti`]

>Given an array, n, of datapoints, such that:
>
>>> size(n)
>rows = 27000
>columns = 2
>
>where n(:,1) are all the integer x values, and n(:,2) are all the
>integer y values, both integer values are in the range of 1 to 101
>
>I slowly did it this way:
>
>output=zeros(101,101);
>for i=1:27000
>  output( n(i,1),n(i,2) ) = output( n(i,1),n(i,2) ) + 1;
>endfor

You are creating a sparse matrix with summation by hand.
It should work like this:

 output = sparse(n(:,1),n(:2),ones(27000,1),101,101);

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