How to obtain an array of the indices from the original array when using nchoosek

5 次查看（过去 30 天）
Kevin H
Kevin H 2023-8-22
评论： Kevin H 2023-8-22
How do I use nchoosek and also efficiently generate an array that has the indices from the original array. For instance,
A = [7, 8, 9]
B = nchoosek(A, 2)
so B = [7, 8; 7, 9; 8, 9]
I want a matrix C that holds the indices in A of all the members of B:
C = [1, 2; 1, 3; 2, 3].
I can generate C using a for loop since we know how nchoosek is going to generate the combinations, but this seems very wasteful precisely because we know how nchoosek is going to generate the combinations, all the information of the indices is already there in our first call of nchoosek. How do I get C efficiently?

请先登录，再回答此问题。

采纳的回答

the cyclist
the cyclist 2023-8-22
编辑：the cyclist 2023-8-22
Ran in:
I have to admit I am not absolutely certain about what you want as input and output. Here is my best guess:
A = [7, 8, 9];
C = nchoosek(1:numel(A),2)
C = 3×2
1 2 1 3 2 3
B = A(C)
B = 3×2
7 8 7 9 8 9

更多回答（1 个）

Torsten
Torsten 2023-8-22
编辑：Torsten 2023-8-22
Ran in:
You better get B from C, not C from B:
A = [7, 8, 9];
v = 1:numel(A);
C = nchoosek(v,2)
C = 3×2
1 2 1 3 2 3
B = A(C)
B = 3×2
7 8 7 9 8 9

类别

在 Help Center 和 File Exchange 中查找有关 Matrices and Arrays 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by