Randomly delete elements of a matrix
1 view (last 30 days)
Show older comments
Hi guys,
how would you, if you have an arbitrary matrix, randomly delete one element in each row and column of said matrix.
So, for example, you start with a matrix A of size 5x5 and you wanna end up with B of size 4x4.
Thanks!
Edit: I tried it like this, but it results in an error:
a = magic(5);
inRow = randperm(size(a,1));
inCol = randperm(size(a,2));
a(inRow,inCol) = [];
1 Comment
Answers (4)
Justace Clutter
on 12 Apr 2013
The problem with what you have tried is that you have to remove the entire column and the row and not just a single element. Try the following code instead
a = magic(5);
rowIndex = randi(size(a, 1), 1);
columnIndex = randi(size(a, 2), 1);
anew = a;
anew(rowIndex,:) = [];
anew(:,columnIndex) = [];
disp(a);
disp(anew);
The Result of this code is the following:
17 24 1 8 15
23 5 7 14 16
4 6 13 20 22
10 12 19 21 3
11 18 25 2 9
17 24 1 8
23 5 7 14
4 6 13 20
10 12 19 21
Justace Clutter
on 12 Apr 2013
Edited: Justace Clutter
on 12 Apr 2013
I have a few followup questions:
1: What do you do in the following case?
x o o x
x x x o
x x x o
Should it be:
x x x x
x x x
x
In the example you provided, it was clean, but I am not sure what to do in this case.
2: Does the order of the elements in the final matrix matter?
Cedric
on 12 Apr 2013
Edited: Cedric
on 12 Apr 2013
Look at the following and let me know if you have any question:
M = randi(10, 4, 5) ; % Random example.
[nr,nc] = size(M) ;
ind = sub2ind([nr,nc], randi(nr, 1, nc), 1:nc) ;
N = M(:) ;
N(ind) = [] ;
N = reshape(N, [], nc) ;
Running this gives e.g.:
>> M
M =
3 2 6 6 6
7 5 3 7 2
7 10 8 9 2
2 4 3 10 3
>> N
N =
3 2 6 7 6
7 10 3 9 2
7 4 8 10 2
PS: if you want to replace M with its reduced version, you don't need to build N; you can just have
[nr,nc] = size(M) ;
ind = sub2ind([nr,nc], randi(nr, 1, nc), 1:nc) ;
M = M(:) ;
M(ind) = [] ;
M = reshape(M, [], nc) ;
2 Comments
Justace Clutter
on 12 Apr 2013
I was thinking about this solution but I was not sure if that is what he was looking for exactly. I was building up to it but you beet me to it. :)
See Also
Categories
Find more on Matrices and Arrays in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!