matlab submatrices in loop

Question

I have a 118800x6 matrix. the first column contains values from 1 to 99 (there are 1200 rows for each value). now I need to create a new matrix that contains 900 random rows (all of the previous column; the rows are extracted from the original matrix) for each 99 values. I tried with a for loop but that means that I have to write 99 rows of code...there is a faster way? Thank you in advance.

The all of the previous column requirement has me puzzled, but I think ‘randperm‘ will help you out. — macduff, Feb 20 '13 at 00:15
Is there any way we can see a sample of what the 99 lines of code might look like? — johnish, Feb 20 '13 at 02:21
@johnish - why would we want to look at these 99 lines of code? — Shai, Feb 20 '13 at 07:20
@Shai - I don't need to see all 99 lines... 50 or 60 would probably be enough for me to get my mind around this. — johnish, Feb 20 '13 at 08:55

score 0 · Accepted Answer · answered Feb 20 '13 at 06:20

assuming your matrix is called M:

for num = 1:99
    %Extract only rows that have the correct number in column one
    subsample = M(M(1, :) == num, :);
    %Randomly change the order of the rows of this subsample
    shuffledsubsample = subsample(randperm(1200), :);
    %Only keep the first 900 rows
    final(:,:,num) = shuffledsubsample(1:900, :);
end

matlab submatrices in loop

1 Answers1