# Bhilding new matrix with selected index number

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Moe on 29 Oct 2014
Answered: Orion on 29 Oct 2014
Suppose I have a matrix a:
a = [9;1;3;2;5;6;8;1;2;5;8;2];
And I have another matrix b which is like some selected index number of matrix a:
b = [4;6;1]; % for example 4 means forth row in matrix a which is 2 here
So, I need to have a new matrix c in that way present those rows in matrix a which are indicated in matrix b and others array be equal to 0:
c = [9,0,0,2,0,6,0,0,0,0,0,0]; % for example first array is 9 because the first row is (1) is in the matrix b and the value is equal 9 because first row in matrix a is 9.

Orion on 29 Oct 2014
just use b as an index vector :
a = [9;1;3;2;5;6;8;1;2;5;8;2];
b = [4;6;1];
c=zeros(1,length(a));
c(b) = a(b);

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