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shuffle_orderby

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Two functions: shuffles vectors or matrices, orders according to a predefined order.

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SHUFFLE Shuffles vectors or matrices.
% SHUFFLE(X) shuffles the elements of a vector or matrix X.
%
% SHUFFLE(X,DIM) shuffles along the dimension DIM.
%
% [Y,I] = SHUFFLE(X) also returns an index matrix I. If X is
% a vector, then Y = X(I). If X is an m-by-n matrix, then
% for j = 1:n, Y(:,j) = X(I(:,j),j); end
%
% Input arguments:
% X - the vector or matrix to shuffle (array)
% DIM - the dimension along which to shuffle (integer)
% Output arguments:
% Y - the vector or matrix with the elements shuffled (array)
% I - the index matrix with the shuffle order (array)
%
% Examples:
% X = [10 25 30 40]
% [Y,I] = SHUFFLE(X)
% Y = 30 25 10 40
% I = 3 2 1 4
%
% X = [10 25 ; 3.2 4.1 ; 102 600]
% [Y,I] = SHUFFLE(X)
% Y = 3.2000 600.0000
% 10.0000 25.0000
% 102.0000 4.1000
% I = 2 3
% 1 1
% 3 2
%
% X = [10 25 50 ; 3.2 4.1 5.5 ; 102 600 455 ; 0.03 0.34 0.01]
% DIM = 1
% [Y,I] = SHUFFLE(X,DIM)
% Y = 10.0000 25.0000 50.0000
% 0.0300 0.3400 0.0100
% 102.0000 600.0000 455.0000
% 3.2000 4.1000 5.5000
% I = 1 4 3 2
%
% X = [10 25 50 ; 3.2 4.1 5.5 ; 102 600 455 ; 0.03 0.34 0.01]
% DIM = 2
% [Y,I] = SHUFFLE(X,DIM)
% Y = 10.0000 50.0000 25.0000
% 3.2000 5.5000 4.1000
% 102.0000 455.0000 600.0000
% 0.0300 0.0100 0.3400
% I = 1 3 2
%
% See also ORDERBY
%
% Created: Sara Silva (sara@itqb.unl.pt) - 2002.11.02

ORDERBY Orders vectors and matrices according to a predefined order.
% ORDERBY(X,I) orders the elements of a vector or matrix X
% according to the index matrix I.
%
% ORDERBY(X,I,DIM) orders along the dimension DIM.
%
% If X is a vector, then Y = X(I). If X is an m-by-n matrix, then
% for j = 1:n, Y(:,j) = X(I(:,j),j); end
%
% Input arguments:
% X - the vector or matrix to order (array)
% I - the index matrix with the ordering to apply (array)
% DIM - the dimension along which to order (integer)
% Output arguments:
% Y - the ordered vector or matrix (array)
%
% Examples:
% X = [10 25 30 40]
% I = [3 2 1 4]
% Y = ORDERBY(X,I)
% Y = 30 25 10 40
%
% X = [10 25 ; 3.2 4.1 ; 102 600]
% I = [2 3 ; 1 1 ; 3 2]
% Y = ORDERBY(X,I)
% Y = 3.2000 600.0000
% 10.0000 25.0000
% 102.0000 4.1000
%
% X = [10 25 50 ; 3.2 4.1 5.5 ; 102 600 455 ; 0.03 0.34 0.01]
% I = [1 4 3 2]
% DIM = 1
% Y = ORDERBY(X,I,DIM)
% Y = 10.0000 25.0000 50.0000
% 0.0300 0.3400 0.0100
% 102.0000 600.0000 455.0000
% 3.2000 4.1000 5.5000
%
% X = [10 25 50 ; 3.2 4.1 5.5 ; 102 600 455 ; 0.03 0.34 0.01]
% I = [1 3 2]
% DIM = 2
% Y = ORDERBY(X,I,DIM)
% Y = 10.0000 50.0000 25.0000
% 3.2000 5.5000 4.1000
% 102.0000 455.0000 600.0000
% 0.0300 0.0100 0.3400
%
% See also SHUFFLE
%
% Created: Sara Silva (sara@itqb.unl.pt) - 2002.11.02

Comments and Ratings (15)

Alex Rogers

######### WARNING #############

shuffle.m resets the random number generator using rand('state',sum(100*clock)) each time it is called.

If you call it repeatedly within a short loop it will continually reset the random number generator seed to the same value and return the same shuffle (and also affect every other random number call within your code). If you are trying to average over stochastic effects this could have disastrous affects.

Alex Rogers

Eve Devaliere

exactly what I was looking for (shuffle) thank you so much!

Pranay Das

thank you very much. this is what I was looking for

doruk bozdag

A Fasih

I needed to have shuffle operate on rows of a matrix, shuffling each row differently, so I changed the last switchcase to

case 1
    [ans,myorder]=sort(rand(size(x)),d);
    bar = repmat((0:size(x,2)-1)*size(x,1),size(x,1),1)+myorder;
    s=x(bar);
case 2
    [ans,myorder]=sort(rand(size(x)),d);
    bar=repmat((0:size(x,1)-1)'*size(x,2),1,size(x,2))+myorder;
    xt=x';
    bar=bar';
    s=xt(bar)';

James Porter

For the 1d case this seems to be more reliable. It should be relatively easy to generalise this.

function [y] = shuffle_better(x)
n = length(x);
r = randperm(n);
    for i = 1:n
        y(r(i)) = x(i);
    end
end

Hector M

Thanks very much!

Fidimahery ANDRIANASY

Bijan Nemati

Shuffle works very efficiently - very handy.

Matthew Salganik

useful and easy -- very helpful

Kaptan Teotrakool

Very efficient. Love it.

Johannes Sarnthein

works nicely

Nathan Funk

Just a note to those that want to shuffle a [1...n] array: there is a built-in function called randperm that will do this for you :)

Nathan

edgarin leon

good job!

MATLAB Release
MATLAB 5.2 (R10)
Acknowledgements

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