CODEWITHSUNDEEP
matlabvectorization
Yuval Atzmon
Yuval Atzmon

Reputation: 5945

How to elegantly sum into repeated indices of a vector in matlab

I am trying to figure out a way to do the following without a loop:

Lets say I have a vector x where I sum some elements e into. I also have a vector of indices ids which say to which elements of x to send the values to. i.e.

x = zeros(1,4);
e = [ 1 10 100 1e3 1e4];
ids = [1 1 2 4 3];

I would like to do something like

x(ids) = x(ids) + e

That will return

x =

          11         100       10000        1000

because we refer to x(1) twice, while instead it returns

x =

          10         100       10000        1000

Upvotes: 0

Views: 105

Answers (1)

Some Guy
Some Guy

Reputation: 1797

accumaray is a really useful function for doing such tricks. In your case:

accumarray(ids',e)

will do the job.

Upvotes: 3

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