Minimum value in sub Matrix

3 次查看（过去 30 天）
Zach Hudson
Zach Hudson 2015-5-26
编辑： Stephen23 2015-5-26
I have a 4 dimensional matrix that represents an array of arrays and I need to find the minimum value and its index in each of the sub arrays. IE I need to call min(example(:)) on example(:,:,1,1), example(:,:,1,2)... example(:,:,1,m), example(:,:,2,1)... example(:,:,2,m)... example(:,:,n,m). Any help with this would be much appreciated.

请先登录，再回答此问题。

采纳的回答

Stephen23
Stephen23 2015-5-26
编辑：Stephen23 2015-5-26
You can just use min with its optional dimension argument:
X = [4D array];
Y = min(min(X,[],1),[],2);
Here is a simple example, with a 3D array:
>> X = reshape(1:24, [2,3,4])
X(:,:,1) =
1 3 5
2 4 6
X(:,:,2) =
7 9 11
8 10 12
X(:,:,3) =
13 15 17
14 16 18
X(:,:,4) =
19 21 23
20 22 24
>> Y = min(min(X,[],1),[],2)
Y(:,:,1) =
1
Y(:,:,2) =
7
Y(:,:,3) =
13
Y(:,:,4) =
19
You can see then it has calculated the minimum of the first two dimensions only, leaving the third dimension remaining. This works for 4D arrays too. If you do not want the leading scalar-dimensions to remain, simply use squeeze to remove them:
>> squeeze(Y)
ans =
1
7
13
19
  2 个评论
Zach Hudson
Zach Hudson 2015-5-26
This works to get the minimum value but I would really like the index as well.
Stephen23
Stephen23 2015-5-26
编辑：Stephen23 2015-5-26
This is possible, but more complicated. Here is an example for a 3D array:
>> X = reshape(randperm(24), [2,3,4])
X(:,:,1) =
7 21 12
20 6 24
X(:,:,2) =
14 3 8
22 10 15
X(:,:,3) =
19 5 16
11 4 1
X(:,:,4) =
13 23 18
2 17 9
>> [Y,idy] = min(X,[],1);
>> [Z,idz] = min(Y,[],2);
>> N = size(X,3);
>> idy(sub2ind(size(idy),ones(N,1),squeeze(idz),(1:N)')) % row indices
ans =
2
1
2
2
>> squeeze(idz) % column indices
ans =
2
2
3
1
>> squeeze(Z) % the minimum values
ans =
6
3
1
2
This can be extended to work with 4D arrays... with some effort. It might be easier to perform this operation independently for each slice of the fourth dimension.

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 Deep Learning Toolbox 的更多信息

标签

产品

Community Treasure Hunt

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

Start Hunting!

Translated by