Generating all ordered samples with replacement

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Riccardo
Riccardo 2019-5-7
评论： Jan 2019-5-8
Hello everybody,
is there a function in Matlab which generates an array containing all ordered samples of length k taken from a set of n elements , that is all the k-tuples where each can be any of the , and whose total number is ?
Or can anybody suggest a simple code to generate all of them? I am guessing it involves the iterative use of datasample function checking that every new generated sample is different from the previous ones, but I couldn't find so far a satisfactory way to write it

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采纳的回答

Jan
Jan 2019-5-7
编辑：Jan 2019-5-7
A fast C-mex: https://www.mathworks.com/matlabcentral/fileexchange/26242-vchoosekro
If you do not have a C-compiler:
function Y = VChooseKRO_M(X, K)
X = X(:);
nX = numel(X);
Y = zeros(nX ^ K, K);
r1 = nX ^ (K - 1);
r2 = 1;
for k = 1:K
Y(:, k) = repmat(repelem(X, r1, 1), r2, 1);
r1 = r1 / nX;
r2 = r2 * nX;
end
end

更多回答（2 个）

Guillaume
Guillaume 2019-5-7
编辑：Guillaume 2019-5-7
For and ,
n = 20;
k = 5;
result = dec2base(0:n^k-1, n); %generate all n^k samples with replacement, as char vector 0-9 + A-Z
result = result - '0' + 1; %convert character to numbers 1-10, A-Z get converted to 18+
result(result>17) = result(result>17) - 7 %convert 18+ to 11+
For greater n you'll have to use Jan's answer.
Riccardo
Riccardo 2019-5-8
What about this solution, I don't know if it's as fast as yours, but do you think is correct?
function Y = ordsampwithrep(X,K)
%ordsampwithrep Ordered samples with replacement
% Generates an array Y containing in its rows all ordered samples with
% replacement of length K with elements of vector X
X = X(:);
nX = length(X);
Y = zeros(nX^K,K);
Y(1,:) = datasample(X,K)';
k = 2;
while k < nX^K +1
temprow = datasample(X,K)';
%checknew = find (temprow == Y(1:k-1,:));
if not(ismember(temprow,Y(1:k-1,:),'rows'))
Y(k,:) = temprow;
k = k+1;
end
end
end
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Riccardo
Riccardo 2019-5-8
Thanks, I have tested with a script for and , and I agree, it's quite slower (around 14 seconds compared with 0.01-0.002 seconds). I just wanted to know if it's formally correct.

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