Comparison between vectors in matlab

Question

if i have A=[3 4 5 6] and B=[6 5 4] then i want to compare each value in A with all values in B, if this value is greater then increase counter with 1 and if this value is equal then increase another counter with 1

Answer 1

If you want an array that corresponds to the result of each value in A, you could do

arrayfun(@(x) sum(x > B), A)

this gives [0, 0, 1, 2]. If you want the total sum you would just put sum(...) around that:

sum(arrayfun(@(x) sum(x > B), A))

this gives 3.

For the equal-counter, you can simply change > to ==:

arrayfun(@(x) sum(x == B), A)

this gives [0, 1, 1, 1].

Answer 2

Another approach in comparison to arrayfun would be bsxfun. Though it takes a bit more memory, I'd argue that it's faster. arrayfun is implicitly a for loop and using loops in MATLAB is usually slower than vectorized approaches.

If you want the greater than case, use the gt function with bsxfun, so:

>> A = [3 4 5 6];
>> B = [6 5 4];
>> sum(bsxfun(@gt, A, B.'), 1)

ans =

     0     0     1     2

If you want to accumulate all of the values that match the criterion, you can put another sum call within this bsxfun call:

>> sum(sum(bsxfun(@gt, A, B.'), 1))

ans =

     3

For the greater than or equal case, use ge:

>> sum(bsxfun(@ge, A, B.'), 1)

ans =

     0     1     2     3

For the equality case, use eq:

>> sum(bsxfun(@eq, A, B.'), 1)

ans =

     0     1     1     1

Again, if you want to accumulate all of the values that match the criterion, nest another sum call with the above results.