如何在R中将矩阵分成较小的矩阵? [英] How can I separate a matrix into smaller ones in R?

问题描述

我有以下矩阵

2    4    1
6    32   1
4    2    1
5    3    2
4    2    2

我想根据第3列制作以下两个矩阵

I want to make the following two matrices based on 3rd column

第一

2    4
6    32
4    2

秒

5    3
4    2

我想出了最好的办法，但出现错误

Best I can come up with, but I get an error

x<-cbind(mat [，1]，mat [，2])如果mat [，3] = 1

x <- cbind(mat[,1], mat[,2]) if mat[,3]=1

y<-如果mat [，3] = 2则cbind(mat [，1]，mat [，2])

y <- cbind(mat[,1], mat[,2]) if mat[,3]=2

推荐答案

如果您有矩阵A，则当第三列为1时，它将获得前两列:

If you have a matrix A, this will get the first two columns when the third column is 1:

A[A[,3] == 1,c(1,2)]

您可以使用它来获取第三列中任何值的矩阵.

You can use this to obtain matrices for any value in the third column.

说明:A [，3] == 1返回一个布尔向量，如果A [i，3]为1，则第i个位置为TRUE.该布尔向量可用于将矩阵索引为:提取我们想要的行.

Explanation: A[,3] == 1 returns a vector of booleans, where the i-th position is TRUE if A[i,3] is 1. This vector of booleans can be used to index into a matrix to extract the rows we want.

免责声明:我对R的经验很少，这是MATLAB式的方法.

Disclaimer: I have very little experience with R, this is the MATLAB-ish way to do it.

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