MATLAB: Reduce one dimension of a array by using sum

for loops

Hello,

Can anyone show me how I can reduce one dimension of the following array without using for loops. Thanks!

A=rand(100,100,100);
for ith = 1:100
    for jth = 1:100
    B(ith,jth) = sum(A(ith,:,jth))
    end
end

If you are summing across the second dimension of your three-dimension array A, the easiest way would be to use the ‘dim’ argument of sum:

B = squeeze(sum(A,2))

Does this do what you want?

A=rand(300,200);
out=sum(A)

A = randi(99,300,300,50); % data
X = randi(50,300,300);    % indices
B = sum(A.*double(reshape(1:50,1,1,[])<=X),3);

For MATLAB versions prior to R2016B replace the <= with bsxfun and le.

Checking one random position (row=2,col=3):

>> X(2,3)
ans =  37
>> sum(A(2,3,1:37))
ans =  1947
>> B(2,3)
ans =  1947