Shuffling elements in a dataset

[jcardoso]

Hi,

I have the need to randomize the order (shuffle) of very large 
datasets. The way I devise, randonly sampling with elimination, is 
not very efficient. Is there a better way, using octave's matrix 
manipulation? 

My way:

    nm = num = rows(data);

    for i=1:num
        rn = ceil(rand * nm--);
        new_data(i,:) = data(rn,:);
        data(rn,:) = [];
    endfor

Better way: perhaps creating a vector of unique indexes? but how to 
do this? 

    idx = 1:rows(data);
    now shuffle idx
    new_data = data(idx,:)

Of course, this it is the same problem in one dimension...

Thanks,
Joao
--
Joao Cardoso, INESC  |  e-mail: address@hidden
R. Jose Falcao 110   |  tel:    + 351 2 2094345
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