查找矩阵中行的排列 [英] Find permutations of rows in matrix

问题描述

我正在编写一段代码，该代码应该在Nx3矩阵E中查找包含Mx3矩阵T的值的行，但是它们不一定是相同的顺序.我写了一些有效的东西，但是我对样式不满意，希望使用ismember和find而不是我正在使用的循环在矩阵上进行逻辑运算:

I am writing a piece of code that is supposed to find the rows in Nx3 matrix E that contains the values of Mx3 matrix T, but they are not necessarily in the same order. I wrote something which is working, but I am not happy with the style and wish to apply logical operations on the matrices using ismember and find, rather than the loop I am using:

E = [7 36 37; 9 1 5; 4 34 100; 4 12 33; 4 34 33];
T = [37 7 36; 4 34 33];      

for i=1:size(T,1)
    T(i,:) = sort(T(i,:));
end

for i=1:size(E,1)
    E(i,:) = sort(E(i,:));
end

res = zeros(size(T,1),1);
for i=1:size(T,1)
    a = ismember(E,t(i,:));    
    res(i,1) = find(sum(a,2)==3);
end

我的想法是对E和T的每一行进行排序，因此它们的顺序相同，然后将每个行与一个循环进行比较.但是，我试图学习以更MATLAB风格编写代码，并希望应用ismember并可能会发现执行相同的操作.像这样:

My idea was to sort each row of E and T, so they will be in the same order and then compare each row with a loop. However, I am trying to learn to write my code in a more MATLAB-style and wish to apply ismember and maybe find to do the same operation. Something like this:

a = sum(ismember(E,T(1,1))~=0,2);
b = sum(ismember(E,T(1,2))~=0,2);
c = sum(ismember(E,T(1,3))~=0,2);
r = find(a&b&c);

还有更优雅的解决方案吗?

Any more graceful solutions?

谢谢！

推荐答案

您可以使用这将产生一个逻辑(布尔)向量，该向量指示矩阵T的哪些行(或其任何排列)出现在矩阵E中.请注意，每一行都是独立排序的，以处理重新排序.

This produces a logical (boolean) vector that indicates which rows of matrix T (or any of their permutations) appear in matrix E. Note that each row is sorted independently to handle reordering.

如果需要T行的索引，请同时使用ismember的两个输出:

If you need the indices of the row of T, use both outputs of ismember:

[tf, loc] = ismember(sort(E, 2), sort(T, 2), 'rows')

注意:如果您的数据包含浮点数，则ismember方法可能会失败，因此您需要设置比较公差.请参见此答案以获取更可靠的替代方法(并记住沿2 ^{nd对输入矩阵进行排序}首先是尺寸！).

Note: if your data contains floating-point numbers, the ismember approach might fail, so you'll need to set a tolerance for comparison. See this answer for a more robust alternative approach (and remember to sort your input matrices along the 2^nd dimension first!).

E = [7 36 37; 9 1 5; 4 34 100; 4 12 33; 4 34 33];
T = [37 7 36; 4 34 33];
[tf, loc] = ismember(sort(E, 2), sort(T, 2), 'rows');

结果是:

tf =          loc =
     1              1
     0              0
     0              0
     0              0
     1              2

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