查找A> B的行的有效方法

问题描述

假设M是一个矩阵，其中每一行代表N个对象池(例如

Suppose M is a matrix where each row represents a randomized sequence of a pool of N objects, e.g.,

1 2 3 4
3 4 1 2
2 1 3 4

如何有效地找到数字B之前数字A的所有行?

How can I efficiently find all the rows in which a number A comes before a number B?

例如A=1和B=2;我想检索第一行和第二行(其中1在2之前)

e.g., A=1 and B=2; I want to retrieve the first and the second rows (in which 1 comes before 2)

推荐答案

去那里:

[iA jA] = find(M.'==A);
[iB jB] = find(M.'==B);
sol = find(iA<iB)

请注意，这样做的原因是，根据问题说明，可以保证每个数字在每一行中都出现一次.

Note that this works because, according to the problem specification, every number is guaranteed to appear once in each row.

要查找具有给定前缀的M行(按注释中的要求):假设prefix是具有所查找前缀的向量(例如，prefix = [1 2]):

To find rows of M with a given prefix (as requested in the comments): let prefix be a vector with the sought prefix (for example, prefix = [1 2]):

find(all(bsxfun(@eq, M(:,1:numel(prefix)).', prefix(:))))

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