# How I can randomly divide my data

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Sehairi K. on 25 Sep 2017
Edited: Jan on 26 Sep 2017
I have a matrix X with size nxm, How I can choose randomly 70 percent of this data and put it in matrix A and the rest in matrix B. I have already selected the 70% (according to rows) using the 'datasample' function, is there any tip to select the rest 30% of the data with there indices
[n,m]=size(X);
[A,idx] = datasample(X,round(0.7*n));

Jan on 25 Sep 2017
Edited: Jan on 25 Sep 2017
[A, idxA] = datasample(X, round(0.7*n));
idxB = 1:n;
idxB(idxA) = [];
B = X(idxB);
This is slightly faster than:
idxB = setdiff(1:n, idxA);
Jan on 26 Sep 2017
Edited: Jan on 26 Sep 2017
In the 2nd line the vector 1:n is created, and in the third line the indices used to create A are removed, such that you get the indices required for B.
The approach with randperm:
row_idx = randperm(n, round(n * 0.7)); % 2 inputs!
A_idx = false(n, 1); % logical(zeros()) wastes time
A = X(A_idx, :);
B = X(~A_idx, :);
I assume that this is faster than with datasample and the index vector.

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