Randomly deleting a 'one' in a column of a binary matrix

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Tim
Tim 2012-10-11
Hi,
I have a matrix that looks like this:
1 1 1 1 1 1
0 1 1 1 1 1
0 0 1 1 1 1
0 0 1 1 1 1
0 0 0 1 1 1
0 0 0 1 1 1
0 0 0 0 1 1
0 0 0 0 1 1
0 0 0 0 0 1
0 0 0 0 0 1
What should I do when I randomly want to delete a 'one' in (let's say) column 4? Thanks in advance,
Tim

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采纳的回答

Wayne King
Wayne King 2012-10-11
编辑：Wayne King 2012-10-11
If you want to just choose one of the 1's from the matrix to set equal to 0, then
indices = find(A>0);
chooseset = randperm(length(indices));
index = chooseset(1);
A(indices(index)) = 0;
If you really want to restrict it to just column 4
indices = find(A(:,4)>0);
chooseset = randperm(length(indices));
index = indices(chooseset(1));
A(index,4) = 0;
Recently randperm() has been updated so you can just get 1 value back.
indices = find(A(:,4)>0);
choice = randperm(length(indices),1);
index = indices(choice);
A(index,4) = 0;

更多回答（1 个）

Azzi Abdelmalek
Azzi Abdelmalek 2012-10-11
编辑：Azzi Abdelmalek 2012-10-11
A=[1 1 1 1 1 1
0 1 1 1 1 1
0 0 1 1 1 1
0 0 1 1 1 1
0 0 0 1 1 1
0 0 0 1 1 1
0 0 0 0 1 1
0 0 0 0 1 1
0 0 0 0 0 1
0 0 0 0 0 1]
m=size(A,2)
idx=randi(m,1)
A(:,idx)=[] % this will remove column number idx
%I 'm not sur what you mean by delete a one, if you want raplace them by 0
A(:,idx)=0
  4 个评论
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Azzi Abdelmalek
Azzi Abdelmalek 2012-10-11
编辑：Azzi Abdelmalek 2012-10-11
Tim you did'nt read all the answer, at the end I said use
A(:,idx)=0
istead of
A(:,idx)=[]
which means use the below code
m=size(A,2)
idx=randi(m,1)
A(:,idx)=0
Tim
Tim 2012-10-11
Hi Azzi,
You're right, I did not read that part of the answer. This will however replace one of the columns with only zeros instead of take one of the '1's from a column. Wayne already helped me with that, but thanks again for your help!
Cheers, T.

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