2d - fast 2dimensional histograming in matlab -

i have written 2d histogram algorithm 2 matlab vectors. unfortunately, cannot figure out how vectorize it, , order of magnitude slow needs. here have:

    function [ result ] = hist2d( vec0, vec1 ) %hist2d takes 2 vectors, , computes 2 dimensional histogram % of images.  assumes vectors non-negative, , bins % integers. % %  outputs %      result -  %         size(result) = 1 + [max(vec0) max(vec1)] %         result(i,j)  = number of pixels have value  %                             i-1 in vec0 , value j-1 in vec1.      result = zeros(max(vec0)+1, max(vec1)+1);      fvec0 = floor(vec1)+1;     fvec1 = floor(vec0)+1;      % ugh, gross, there has better way...     = 1 : size(fvec0);         result(fvec0(i), fvec1(i)) = 1 + result(fvec0(i), fvec1(i));     end end 

thoughts?

thanks!! john

here version 2d histogram:

%# random data x = randn(2500,1); y = randn(2500,1)*2;  %# bin centers (integers) xbins = floor(min(x)):1:ceil(max(x)); ybins = floor(min(y)):1:ceil(max(y)); xnumbins = numel(xbins); ynumbins = numel(ybins);  %# map x/y values bin indices xi = round( interp1(xbins, 1:xnumbins, x, 'linear', 'extrap') ); yi = round( interp1(ybins, 1:ynumbins, y, 'linear', 'extrap') );  %# limit indices range [1,numbins] xi = max( min(xi,xnumbins), 1); yi = max( min(yi,ynumbins), 1);  %# count number of elements in each bin h = accumarray([yi(:) xi(:)], 1, [ynumbins xnumbins]);  %# plot 2d histogram imagesc(xbins, ybins, h), axis on %# axis image colormap hot; colorbar hold on, plot(x, y, 'b.', 'markersize',1), hold off 

note removed "non-negative" restriction, kept integer bin centers (this changed dividing range equally-sized specified number of bins instead "fractions").

this inspired @steveeddins blog post.