how to generate permutations of N numbers in K positions

108 次查看（过去 30 天）
Ali Danish
Ali Danish 2019-2-19
评论： Subzero 2023-3-31
I want to generate all permutations of N numbers in K places, where K is less than N (nPk) in matlab, I've searched online and already existing questions but couldn't find a functions which generates such permutations without repitition. There are some functions which do this with repitation.
For example if I've a vector [1 2 3 4] my N is 4 and my K is 2, then I want 12 permutations using the formula N!/(N-K)1 = 4!/(4-2)! = 12
[1,2]
[1,3]
[1,4]
[2,1]
[2,3]
[2,4]
[3,1]
[3,2]
[3,3]
[4,1]
[4,2]
[4,3]
These are the permutations which I want to generate. Kindly suggest me the solution.

请先登录，再回答此问题。

采纳的回答

Stephen23
Stephen23 2019-2-19
编辑：Stephen23 2019-2-19
Download Loginatorist's powerful FEX submission combinator:
https://www.mathworks.com/matlabcentral/fileexchange/24325-combinator-combinations-and-permutations
and use it like this:
>> sortrows(combinator(4,2,'p'))
ans =
1 2
1 3
1 4
2 1
2 3
2 4
3 1
3 2
3 4
4 1
4 2
4 3
If you want to apply this to a vector that is not 1:N, simply use the output of combinator as indices into your vector.

更多回答（2 个）

Bruno Luong
Bruno Luong 2021-3-22
编辑：Bruno Luong 2021-3-22
Ran in:
No loop, no extrenal file needed
N=5; K=3;
P=nchoosek(1:N,K);
P=reshape(P(:,perms(1:K)),[],K)
P = 60×3
3 2 1 4 2 1 5 2 1 4 3 1 5 3 1 5 4 1 4 3 2 5 3 2 5 4 2 5 4 3
You might further sort the permutation so that the order is easily to follow
P = sortrows(P)
P = 60×3
1 2 3 1 2 4 1 2 5 1 3 2 1 3 4 1 3 5 1 4 2 1 4 3 1 4 5 1 5 2
  4 个评论
显示 2更早的评论
Walter Roberson
Walter Roberson 2022-11-24
@Subzero
If you have an array P that is 2 or more dimensions (not a vector!), and you use P(A,B) where A and B might be arrays, then the result is the same as if you had used P(A(:), B(:)) -- so P(A(1),B(1)), P(A(2),B(1)), P(A(3),B(1)) up to P(A(end),B(1)) is the first column, then the second column would be P(A(1),B(2)), P(A(2),B(2)), P(A(3),B(2)) to P(A(end),B(2)), and so on -- all combinations of the elements in A with all of the elements in B, same as if A and B had been vectors rather than 2D arrays.
The shape of the result might be different if P is a vector instead of a 2D array.

请先登录，再进行评论。

Sergey Kasyanov
Sergey Kasyanov 2021-3-22
Hello!
Use nchoosek function with combination of perms function. That solution is slow but does not require any side files.
res = nchoosek(1:4, 2);
for i = 1:size(res,1)
res = [res; perms(res(i,:))];
end
res = unique(res, 'rows');

类别

在 Help Center 和 File Exchange 中查找有关 Discrete Math 的更多信息

标签

产品


版本

R2013b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by