How do I efficiently add values of same indices to a vector?

Question

Tzaki 2022-1-25

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https://ww2.mathworks.cn/matlabcentral/answers/1635760-how-do-i-efficiently-add-values-of-same-indices-to-a-vector

编辑： Tzaki 2022-1-25

Hello, I am pretty much new to MATLAB.

I have a large vector vec1=[2 7 4 3], a small vector vec2=[1 10 100], and an index vector ind=[1 2 1] (numel(vec2)=numel(idx)). I want to add each element of vec2 to the element of vec1 that is specified by ind. In this example, I want ans=[103 17 4 3].

Intuitively, I first tried

vec1(ind) = vec1(ind) + vec2, (1)

but this gave me ans=[102 17 4 3], telling me that the duplicates in ind were not considered.

To get around this, I added a for loop before (1) to remove the duplicates, which works fine but takes too long.

I would like to know if there is an efficient way to solve this.