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how to randomize a vector as fast as possible

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eden kisos
eden kisos on 8 Dec 2019
hello;
I have this vector:
0.001:0.001:125 (size 125000)
I would like to shuffle it as fast as possible because this function repeates alot in my code (without using randperm and such because it is really slow, I dont have the shuffle function on my computer)
any ideas?
thanks :)

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Answers (2)

Stijn Haenen
Stijn Haenen on 8 Dec 2019
this is finished in 28 sec, i dont know how fast other methods are.
tic
Vec=1:125000;
numelVec=numel(Vec);
new_Vec=zeros(1,numelVec);
for i=1:numelVec
rand_num=datasample(Vec,1);
Vec(Vec==rand_num)=[];
new_Vec(i)=rand_num;
end
toc

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JESUS DAVID ARIZA ROYETH
JESUS DAVID ARIZA ROYETH on 8 Dec 2019
this for loop would be much slower than randperm:
tic
shuflle=Vec(randperm(125000));
toc
eden kisos
eden kisos on 8 Dec 2019
the loop is too slow for me. I am doing it more that 1000000 times. randperm is even slower
i tried this way but it is still runs slow:
jump= 0.001:0.001:125
[~,randomly]=sort(rand(1,length(jump),1),2);
[~,order]= sort (randomly);
jump=jump(order);
JESUS DAVID ARIZA ROYETH
JESUS DAVID ARIZA ROYETH on 8 Dec 2019
this is much faster than what you currently have:
jump= 0.001:0.001:125
jump=jump(randperm(125000));

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JESUS DAVID ARIZA ROYETH
JESUS DAVID ARIZA ROYETH on 8 Dec 2019
I recommend using a MEX file https://ww2.mathworks.cn/matlabcentral/fileexchange/27076-shuffle?s_tid=FX_rc3_behav if you want to do the process much faster, here you can download this file and add it to your folder, do mex Shuffle.c for once on your matlab console, and you can now use a function much faster than randperm , you could compare it as follows:
Vec=1:125000;
tic
shuflle=Vec(randperm(125000));%normal
toc
tic
shuflle2=Shuffle(Vec);%with mex file
toc

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eden kisos
eden kisos on 8 Dec 2019
I tried to use this function and this is the warnning I get: Need compiled mex file!
JESUS DAVID ARIZA ROYETH
JESUS DAVID ARIZA ROYETH on 8 Dec 2019
first of all you need run mex Shuffle.c in your matlab command window
mex Shuffle.c
and if you don't have a supported compiler then you need to install it following the instructions that matlab gives you in the error

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