choose 2 random unique element inside cell

Question

NA 2019-2-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/446569-choose-2-random-unique-element-inside-cell

评论： Jos (10584) 2019-2-25

how to choose 2 random unique element inside a cell?

index={[1,2,5,9,10,13,17,18,21],[4,5,7,12,13,15,18,20,21],[3,4,6,11,12,14,18,19,20],[8,16,20,22]};

example of result

p={[1,9],[7,21],[3,4],[16,8]}

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Answer 1

per isakson 2019-2-23

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https://ww2.mathworks.cn/matlabcentral/answers/446569-choose-2-random-unique-element-inside-cell#answer_362374

编辑：per isakson 2019-2-23

在 MATLAB Online 中打开

See datasample, Randomly sample from data, with or without replacement

and try

>> cellfun( @(row) datasample( row, 2, 'replace',false ), index, 'uni',false )
ans =
  1×4 cell array
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}

"[...] random unique element inside a cell" does that mean without replacement?

If it means literal "unique elements" then run this is a first step to remove duplicates.

>> index = cellfun( @unique, index, 'uni',false )
ix =
  1×4 cell array
    {1×9 double}    {1×9 double}    {1×9 double}    {1×4 double}

Or should the propability to pick a specific value be proportional to the number of duplicates of that value?

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per isakson 2019-2-24

编辑：per isakson 2019-2-24

在 MATLAB Online 中打开

Problem: You have a working script that runs the simulation once and you want to run it automatically many times

The first approach you shall consider is a for-loop.

Convert the script to a function
Create a second function that calls the first many times
Run the second function

Example

>> out = cssm( index, 5 )
out =
  5×1 cell array
    {1×4 cell}
    {1×4 cell}
    {1×4 cell}
    {1×4 cell}
    {1×4 cell}
>> out{3}
ans =
  1×4 cell array
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}

where

function  out = cssm( index, n )  
    out = cell( n, 1 );
    for jj = 1 : n
        out{jj} = run_once( index );
    end
end
function  out = run_once( index )
    out = cellfun( @(row) datasample( row, 2, 'replace',false ) ...
                  , index, 'uni',false );
end

BTW:

%%
index = repmat( index, 5,1 );
out = cellfun( @(row) datasample( row, 2, 'replace',false ), index, 'uni',false )

outputs

out =
  5×4 cell array
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}
    {1×2 double}    {1×2 double}    {1×2 double}    {1×2 double}

NA 2019-2-24

编辑：per isakson 2019-2-24

amount is calculated by adding normrnd. so it changes in each iteration.

per isakson 2019-2-24

"amount is calculated by adding normrnd" That means that you need to be careful regarding Accuracy of Floating-Point Data

So far, I have assumed whole numbers

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Answer 2

Jos (10584) 2019-2-23

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https://ww2.mathworks.cn/matlabcentral/answers/446569-choose-2-random-unique-element-inside-cell#answer_362380

在 MATLAB Online 中打开

If I understand you correctly, the final output should have 8 unique numbers, in four groups of two, where the numbers in each group is drawn from a cell in the cell array index. This is not a trivial problem to answer! There might situations where this is simply impossible given a cell array index (for instance index= {[1 2 3], [1 2 4], [2 3 4],... }

You might want to try a brute-force method

index={[1,2,5,9,10,13,17,18,21],[4,5,7,12,13,15,18,20,21],[3,4,6,11,12,14,18,19,20],[8,16,20,22]};
fn = @(v) sort(v(randperm(numel(v),2))) ; % function to draw 2 randomelements from v
k = 1 ;
while k < 1e5 % try a lot of times
    C = cellfun(fn, index,'un',0) ;
    if numel(unique([C{:}])) == 8,
        break
    else
        C = [] ; k = k+1 ;
    end
end
celldisp(C)