fastest way of matching a number in an array
in [Matlab]
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From: Judy on 3 Mar 2010 15:04 Thank you for all your inputs! :)
From: Jan Simon on 3 Mar 2010 15:22 Dear Judy! > I am looking for any 5's and want to see if there is a quick way to check if there is a 5 in a large array -- i.e. a=zeros(100,100); a(23,64)=5; While ISMEMBER is not really fast, Matt's method is efficient: any(a(:) == 5) If you are working on 100x100 arrays, the efficiency should be enough. But if you process thousands of arrays with 100MB, a C-Mex can be dramatically faster: a(:)==5 compares all elements of the array, but if the first element is 5 the processing can be stopped early! Kind regards, Jan
From: Jan Simon on 8 Mar 2010 18:55
Dear Judy! For X with more than about 10'000 elements this C-Mex is faster than ANY(X==y) even in the worst case that y is not a membor of X: http://www.mathworks.com/matlabcentral/fileexchange/26867 This function stops the comparison after the first match. Therefore for large arrays. e.g. 1E7 elements and if y appears early in X, it is much more efficient than ANY(X==y). Good luck, Jan |