（Matlab）使用min函数返回的索引进行维度索引 [英] (Matlab) Dimensional indexing using indices returned by min function

问题描述

假设我有一个5维矩阵C.我使用下面的代码得到一个min矩阵C3（C3的每个元素代表维度1,2,3的最小值）：

  [C1，I1] = min（C，[]，1）; 
 [C2，I2] = min（C1，[]，2）; 
 [C3，I3] = min（C2，[]，3）; 
  

问题是如何获得每个维度的最小索引？例如，考虑这个更简单的情况：

  C = [1,2; 3,4] 
  

此处的最小值为1，维度1中的索引为1（第一行），维度2中的索引也为1（第一列）。 / p>

我知道改变这些表达式的顺序会给我正确的答案，但是如果我想通过只计算一次这些表达式来获得所有维数索引呢？

解决方案

将此用于5D矩阵 -

  [〜，ind] = min（C（:)）
 [ind_dim1，ind_dim2，ind_dim3，ind_dim4，ind_dim5] = ind2sub（size（C），ind）
  

编辑1：这是针对您不是在寻找全局但特定维度的最小值和索引的情况。

代码

  %% //演示的随机数据
 C = randi（60,2,3,4,2,3）; 
 
 %% //你的方法
 [C1，I1] = min（C，[]，1）
 [C2，I2] = min（C1，[]， 2）
 [C3，I3] = min（C2，[]，3）
 
 %% //我的方法
 dimID = 3; %% //尺寸，直到找到最小值
 C_size = size（C）; 
 dim_v1 = prod（C_size（1：dimID））
 dim_v2 = prod（C_size（1：dimID-1））
 
 t1 =重塑（C，[dim_v1 C_size（ dimID + 1：end）]）
 [val，ind1] = min（t1，[]，1）
 chk1_ind = ceil（ind1 / dim_v2）
 
 %% / /这可能就足够了，但是你坚持要获得格式为
 %% //的索引与从你的方法获得的索引相同，请尝试下一步
 
 C_size（1： dimID）= 1; 
 chk2_ind = reshape（chk1_ind，C_size）
 
 %% //验证
 error_check = isequal（chk2_ind，I3）
  

Suppose I have a 5-d matrix C. I use the following code to get a min matrix C3 (each element of C3 represents the minimum of dimension 1,2,3):

[C1, I1] = min(C,[],1);
[C2, I2] = min(C1, [], 2);
[C3, I3] = min(C2, [], 3);

The question is how to get the index of the minimum in terms of each dimension? For example consider this simpler case:

C = [1,2;3,4]

The minimum here is 1, its index in dimension 1 is 1 (first row) and in dimension 2 also 1 (first column).

I know that changing the sequence of these expressions would give me the right answer, but what if I want to get all dimensional indices with computing these expressions only once?

解决方案

Use this for a 5D matrix -

[~,ind] = min(C(:))
[ind_dim1,ind_dim2,ind_dim3,ind_dim4,ind_dim5] = ind2sub(size(C),ind)

Edit 1: This is for a case where you are not exactly looking for global but dimension specific minimum values and indices.

Code

%%// Random data for demo
C = randi(60,2,3,4,2,3);

%%// Your method
[C1, I1] = min(C,[],1)
[C2, I2] = min(C1, [], 2)
[C3, I3] = min(C2, [], 3)

%%// My method
dimID = 3; %%// Dimension till when minimum is to be found out
C_size = size(C);
dim_v1 = prod(C_size(1:dimID))
dim_v2 = prod(C_size(1:dimID-1))

t1 = reshape(C,[dim_v1 C_size(dimID+1:end)])
[val,ind1] = min(t1,[],1)
chk1_ind = ceil(ind1/dim_v2)

%%// This might suffice for you, but you insist to get the indices in the format 
%%// identical to the one obtained from your method, try the next steps

C_size(1:dimID)=1;
chk2_ind = reshape(chk1_ind,C_size)

%%// Verify
error_check = isequal(chk2_ind,I3)

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