Repeat row of a matrix

Question

dan berkowitz 2017-10-22

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https://ww2.mathworks.cn/matlabcentral/answers/362647-repeat-row-of-a-matrix

评论： Cedric 2017-10-23

Hi,

I have a 3x1 array, a = [1 2 3]', and B, a 3x2 matrix.

How can I create C, a 6x2 matrix, whose first row is the same as B and repeated once [a(1)], the second row is the second row of B repeated twice [a(2)], and the third row is the third row of B repeated three times [(a(3)]? I'm trying to use the repelem function but am a bit stuck...Do I have to loop to do this, or is there another way?

Any help would be appreciated. Thx in advance,

DB

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Answer 1

Cedric 2017-10-22

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Here is one way to achieve it. If

 >> a = [1;2;3] ;
 >> B = randi( 10, 3, 2 )
 B =
     3    10
     6     2
    10    10

Then

 >> C = arrayfun( @(k)repelem(B(k,:),a(k),1), 1:numel(a), 'UniformOutput', false ) ;
 >> C = vertcat( C{:} )
 C =
     3    10
     6     2
     6     2
    10    10
    10    10
    10    10