一维矩阵变为R中的向量 [英] 1-dimensional Matrix is changed to a vector in R

问题描述

> a<-matrix(c(1:9),3,3)
> a
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9
> a[3,]*a[,3]  # I expect 1x1 matrix as result of this.
[1] 21 48 81
> class(a)
[1] "matrix"
> class(a[3,])
[1] "integer"

在R中，一维矩阵变成了向量.我可以避免这种情况吗?我想将一维矩阵保留为矩阵.实际上，我需要向 RcppArmadillo 抛出多种矩阵，甚至是零维矩阵.将矩阵本身更改为向量是我的问题.

In R, 1-dimensional matrix is changed to a vector. Can I avoid this? I would like to keep 1-D matrix as a matrix. Actually, I need to throw many kind of matrix to RcppArmadillo, even zero-D matrix. Changing matrix to vector by itself is my problem.

推荐答案

这是一个 R 常见问题解答.你需要做a[3,,drop = FALSE].

This is an R FAQ. You need to do a[3,,drop = FALSE].

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