Re: How do I replace this "for" loop?

[Keith Goodman]

How much time does the extra find step add?

>> N = 1000; x = rand(N); tic; x = 2*(x>0);toc
ans = 0.029154
>> N = 1000; x = rand(N); tic; x = 2*(x>0);toc
ans = 0.028811
>> N = 1000; x = rand(N); tic; x = 2*(x>0);toc
ans = 0.028760

>> N = 1000; x = rand(N); tic; idx = find(x>0);x(idx) = 2*x(idx);toc
ans = 0.59328
>> N = 1000; x = rand(N); tic; idx = find(x>0);x(idx) = 2*x(idx);toc
ans = 0.59345
>> N = 1000; x = rand(N); tic; idx = find(x>0);x(idx) = 2*x(idx);toc
ans = 0.59398

If your matrix is big, avoid the find step.



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