在Matlab中矩阵行上向量化直方图

Question

Hello I need to calculate a histogram for every row in a big matrix. For the first row for example I get this:

AA = hist(symbolic_data(1,:), 1:8);

With symbolic_data(1,:)=[7 6 7 8 7] , I get AA=[0 0 0 0 0 1 3 1] .

Of course this is easy using a simple for loop, but my symbolic_data matrix is really big. Is there a way to vectorize this. I've been fiddling with bsxfun , but I can't make it work. Any help would be much appreciated. Thanks for your time.

Answer 1

From Matlab help:

N = hist(Y) bins the elements of Y into 10 equally spaced containers and returns the number of elements in each container. If Y is a matrix, hist works down the columns.

so:

AA = hist(symbolic_data', 1:8);

will do what you want

Answer 2

The answer by @Mercury is the way to go. But if you want to do it with bsxfun :

1. If you only have integer values, use

    bin_centers = 1:8; AA = squeeze(sum(bsxfun(@eq, permute(symbolic_data,[2 3 1]), bin_centers(:).'))); 

2. If the values are not necessarily integer:

    bin_centers = 1:8; AA = squeeze(sum( bsxfun(@le, permute(symbolic_data,[2 3 1]), bin_centers(:).'+.5) &... bsxfun(@gt, permute(symbolic_data,[2 3 1]), bin_centers(:).'-.5) ));