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how to form a new matrix (i.e. B) from two different matrices (i.e. a1, a2) knowing the indices of its origional matrix (indices of a)?

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% a = [1 2 3 4 5 6 7; 2 4 6 8 10 12 14]; % dimension: 2x7
a1 = [2 6 12]; % index in a = [1 3 6] % dimension: 1x3
a2 = [4 8 10 14]; % index in a = [2 4 5 7] % dimension: 1x4
% Now how to form a new matrix "B" such that B = [2 4 6 8 10 12 14]; using a1 and a2. % dimension: 1x7
% Here we know the position of each index in a1 and a2 to be put in new matrix B.
So, how to form a new matrix (i.e. B) from two different matrices (i.e. a1, a2) knowing the indices of its origional matrix (indices of a)?

Accepted Answer

Stephen Cobeldick
Stephen Cobeldick on 25 Feb 2021
Edited: Stephen Cobeldick on 25 Feb 2021
You can use those indices on the left-hand side. For example:
a1 = [2,6,12];
x1 = [1,3,6];
a2 = [4,8,10,14];
x2 = [2,4,5,7];
% Try
b = [a1,a2];
b([x1,x2])= b
b = 1×7
2 4 6 8 10 12 14
% Or
b = nan(1,7);
b(x1) = a1;
b(x2) = a2
b = 1×7
2 4 6 8 10 12 14

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