Use a vector as an index

18 次查看（过去 30 天）
Michael B.
Michael B. 2014-11-5
评论： Michael B. 2014-11-6
I have a matrix of variable dimension and would like to access it with an index stored in a variable, something like this:
matrix = [1, 2; 3, 4; 5, 6]
idx = [3, 1]
elem = matrix(idx) % should result in access to element (3, 1) => 5
Of course, this does not work and will instead get element numbers 3 and 1 (which have values 3 and 1 in that case).
I know sub2ind, but that does not help either, since the number of dimensions is variable. Is there a built-in solution for my problem or will I have to write an access method by myself? (It's not too difficult, but a built-in solution would be preferable.)

请先登录，再回答此问题。

采纳的回答

Guillaume
Guillaume 2014-11-5
You can use cell expansion to comma separated list to index your matrix. So first convert your index matrix into a cell array, then convert the cell array into a list:
c = num2cell(idx);
matrix(c{:}); %expand c into comma separated list
  5 个评论
显示 3更早的评论
Guillaume
Guillaume 2014-11-5
I agree. Unfortunately, the way matlab is designed prevents any simpler method.
Saying that, you can always write your own helper function based on this:
function v = matindex(matrix, vecidx)
%MATINDEX use vector vecidx as an nD index intro matrix to return value v
cidx = num2cell(vecidx);
v = matrix(cidx{:});
end
Michael B.
Michael B. 2014-11-6
And that's exactly why I wonder even more about the lack of a built-in way to do it - it would be so simple.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 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