为什么colMeans / rowMeans的暗淡返回null？

Question

我是R.的新手。我有以下代码

sigma1  = matrix(c(2,0,0,1),2,2)
mu1     = matrix(c(0,10),2,1)

x1      = t(mvrnorm(n = 5, mu1, sigma1))

print(rowMeans(x1))
print(dim(colMeans(x1)))

由于某种原因，我得到了行/ col的维度的NULL。

Answer 1

＆＃39; as.matrix＆＃39;转动矢量＆＃39; colMeans（x1）＆＃39;到一个矩阵。然后尺寸为5和1，如预期的那样：

library(rockchalk)

sigma1  = matrix(c(2,0,0,1),2,2)
mu1     = matrix(c(0,10),2,1)
x1      = t(mvrnorm(n = 5, mu1, sigma1))

print(rowMeans(x1))
print(dim(colMeans(x1)))
print(dim(as.matrix(colMeans(x1))))

输出：

> print(rowMeans(x1))
[1] -0.1518187  9.4232239

> print(dim(colMeans(x1)))
NULL

> print(dim(as.matrix(colMeans(x1))))
[1] 5 1
> 

Answer 2

如果您真的想将矢量强制转换为矩阵，可以尝试类似：

##  Initial Computations.
sigma1  = matrix(c(2,0,0,1),2,2)
mu1 = matrix(c(0,10),2,1)
x1 = t(mvrnorm(n = 5, mu1, sigma1))

##  Coerce the vector of colMeans into a 1 by 5 matrix.
colmeans.x1 = rbind(colMeans(x1))

##  Inspect the dimensions of the matrix created above.
dim(colmeans.c1)

希望有帮助...