两个向量的映射ID [英] Mapping ids of two vectors

问题描述

我有两个具有相同元素的向量，但它们的顺序不相同.对于例如

I have two vectors with the same elements but their order is not same. For eg

A

10
9 
8

B

8
9
10

我想找到两者之间的映射

I want to find the mapping between the two

B2A

3
2
1

如何在matlab中有效地做到这一点?

How can I do this in matlab efficiently?

推荐答案

我认为Matlab排序是有效的.所以:

I think the Matlab sort is efficient. So:

[~,I]=sort(A); %sort A; we want the indices, not the values
[~,J]=sort(B); %same with B
%I(1) and J(1) both point to the smallest value, and a similar statement is true 
%for other pairs, even with repeated values.

%Now, find the index vector that sorts I
[~,K]=sort(I);

%if K(1) is k, then A(k) is the kth smallest entry in A, and the kth smallest 
%entry in B is J(k)
%so B2A(1)=J(k)=J(K(1)), where BSA is the desired permutation vector

% A similar statement holds for the other entries
%so finally

B2A=J(K); 

如果上述内容在脚本"findB2A"中，则应检查以下内容

if the above were in script "findB2A" the following should be a check for it

N=1e4;
M=100;
A=floor(M*rand(1,N));
[~,I]=sort(rand(1,N));
B=A(I);
findB2A;
all(A==B(B2A))

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