MATLAB: How to repeat the rows of a matrix by a varying number

matricesmatrixmatrix arraymatrix manipulation

Hi, I have a matrix A mxn and a matrix B mx1. I want to create a matrix C which repeats each row of A by the number of times indicated in B without looping, e.g.

A=[2 1; 3 4; 5 6; 8 2] 
B=[1;2;4;1]
C=[2 1; 3 4; 3 4; 5 6; 5 6; 5 6; 5 6; 8 2]

Thanks!

Best Answer

A = [2 1; 3 4; 5 6; 8 2] 
B = [1;2;4;1]
C = cell2mat(arrayfun(@(k) A(repmat(k,B(k),1),:), 1:size(A,1), 'un', 0).')

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A=[1 2; 7 8; 5 6; 3 4];
B=[1; 4; 3; 2];
A = A(B,:);

MATLAB: Is there a function to turn ?x2 matrix of coordinates of vertices of a polygon into a ?x4 matrix of coordinates of line segments of that polygon

Yes,

circshift will do the job:

A = [2, 4; 5, 6; 6, 6; 8,5]
B = [2, 4, 5, 6; 5, 6, 6, 6; 6, 6, 8, 5; 8, 5, 2, 4]
% The solution:
C = [A circshift(A,-1)]
% The test:
A =
     2     4
     5     6
     6     6
     8     5
B =
     2     4     5     6
     5     6     6     6
     6     6     8     5
     8     5     2     4
C =
     2     4     5     6
     5     6     6     6
     6     6     8     5
     8     5     2     4

Best Answer

Related Solutions

MATLAB: How to sort a matrix by a predefined order

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