Finding (multiset) difference between two arrays

Question

Given arrays (say row vectors) A and B, how do I find an array C such that merging B and C will give A?

For example, given

A = [2, 4, 6, 4, 3, 3, 1         


        

Answer 1

Still another approach using the histc function:

A = [2, 4, 6, 4, 3, 3, 1, 5, 5, 5];
B = [2, 3, 5, 5];

uA  = unique(A);
hca = histc(A,uA); 
hcb = histc(B,uA);
res = repelem(uA,hca-hcb)

We simply calculate the number of repeated elements for each vectors according to the unique value of vector A, then we use repelem to create the result.

This solution do not preserve the initial order but it don't seems to be a problem for you.

I use histc for Octave compatibility, but this function is deprecated so you can also use histcounts