选择单行矩阵作为矩阵

Question

这一直困扰着我。请考虑以下事项：

# Part A #
# Make a silly simple matrix with column names
x = matrix(1:4, ncol = 2)
colnames(x) = c("a","b")

# Part B #
# Pick out the first row of the matrix.  This is not a matrix, 
#   and the column names are no longer accessible by colnames()
y = x[1,]
y
is.matrix(y)
colnames(y)

# Part C #
# But here is what I want:
y = matrix(x[1,], nrow = 1, dimnames = list(c(), colnames(x)))

有没有办法用更少的处理步骤或更少的代码来实现C部分？似乎应该有一个几乎与x[1,]一样短的命令来做同样的事情。

Answer 1

只需设置drop=FALSE，如下所示：

> y = x[1,, drop=FALSE]
> y
     a b
[1,] 1 3

Answer 2

怎么样

x[1,,drop=FALSE]
     a b
[1,] 1 3