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Repeat row of a matrix

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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

Accepted Answer

Cedric Wannaz
Cedric Wannaz on 22 Oct 2017
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

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