Random order of rows Matlab

Question

Say we have a matrix of size 100x3

How would you shuffle the rows in MATLAB?

Solution 1

To shuffle the rows of a matrix, you can use RANDPERM

shuffledArray = orderedArray(randperm(size(orderedArray,1)),:);

randperm will generate a list of N random values and sort them, returning the second output of sort as result.

Solution 2

This can be done by creating a new random index for the matrix rows via Matlab's randsample function.

matrix=matrix(randsample(1:length(matrix),length(matrix)),:);

Solution 3

While reading the answer of Jonas I found it little bit tough to read, tough to understand. In Mathworks I found a similar question where the answer is more readable, easier to understand. Taking idea from Mathworks I have written a function:

function ret = shuffleRow(mat)

[r c] = size(mat);
shuffledRow = randperm(r);
ret = mat(shuffledRow, :);

Actually it does the same thing as Jonas' answer. But I think it is little bit more readable, easier to understand.

Solution 4

For large datasets, you can use the custom Shuffle function

It uses D.E. Knuth's shuffle algorithm (also called Fisher-Yates) and the cute KISS random number generator (G. Marsaglia).

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Comments

[Jonas]

possible duplicate of How do I randomly select k points from N points in MATLAB?

[edgarmtze]

It is not about selecting, it is about "desorder" or shuffle the rows of a matrix

[Jonas]

Actually, you're right. It's not quite the same question. See my answer below.

[KnowledgeBone]

Your solution runs about 2.5x faster than mine does, at least on my computer.

[Jonas]

I think you meant to use 'false' - if sampling with replacement, the resulting matrix will contain duplicate rows, while others will have disappeared. In the case sampling without replacement, randsample calls randperm, which should thus only be marginally slower than calling randperm directly.

[Rainymood]

Thanks Jonas. Works like a charm. If you instead want to shuffle the columns of a matrix the solution is: shuffledArray = orderedArray(:,randperm(size(orderedArray,2)))