1D array values to 2D matrix

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Eduardo Santos
Eduardo Santos on 8 Apr 2019
Commented: Eduardo Santos on 4 Jan 2021
I would like to 'convert' a 1D array to a 2D matrix considering the value inside the array as:
A =
1 3 5 4 3
B =
1 3 5 4 3
0 3 5 4 3
0 3 5 4 3
0 0 5 4 0
0 0 5 0 0
Can you suggest a fast way to do that?

Accepted Answer

Adam Danz
Adam Danz on 8 Apr 2019
A for-loop would make a cleaner read (I could provide that upon request) but here's two lines the do the trick.
base = cellfun(@(x)repmat(x,x,1), num2cell(A), 'UniformOutput', false);
cell2mat(cellfun(@(y,n) padarray(y,n, 'post'),base, num2cell(max(A)-A), 'UniformOutput', false))
ans =
1 3 5 4 3
0 3 5 4 3
0 3 5 4 3
0 0 5 4 0
0 0 5 0 0
  6 Comments
Adam Danz
Adam Danz on 27 Dec 2020
A = [1,3,5,4,3]
A = 1×5
1 3 5 4 3
B = zeros(max(A),numel(A));
for i = 1:numel(A)
B(1:A(i),i) = 1:A(i);
end
disp(B)
1 1 1 1 1 0 2 2 2 2 0 3 3 3 3 0 0 4 4 0 0 0 5 0 0
Eduardo Santos
Eduardo Santos on 4 Jan 2021
Hi Adam, thanks for the answer. I was wondering something like your previous version but it works anyway.

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