CODEWITHSUNDEEP
matlaboctave
Oleg Pavliv
Oleg Pavliv

Reputation: 21152

sum over indexes

Suppose I have 

A = [10 20 30 40];
idx = [1 1 1 2];
result = [0 0];

I need to sum A over indexes in idx so that 

result(1) = A(1) + A(2) + A(3);
result(2) = A(4);

I implemented the code 

for i=1:length(idx)
  result(idx(i)) += A(i);
end

How can I transform it to more octave-standard code, if possible one-liner?

Upvotes: 4

Views: 4462

Answers (1)

Gunther Struyf
Gunther Struyf

Reputation: 11168

Take a look at accumarray, it does exactly what you are asking for, it only needs its first input as a column:

A = [10 20 30 40];
idx = [1 1 1 2];
result = accumarray(idx',A)

  result =

      60
      40

and yes, this also works in octave ;) (link)

Upvotes: 2

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