Question

我有一个R脚本，通过标量乘法系统地对3x3矩阵进行更改，如下所示

R <- matrix(rexp(9, rate=.1), ncol=3);
for (i in 1:360) {
K = i*R;
...
}

并使用修改后的矩阵在循环内进一步计算。但是，循环本身嵌套在另外两个for循环中，使得脚本非常慢。所以我的问题是，我怎样才能对这个最内层的循环进行矢量化，这样结果就是一个大小为3x3x360的三维数组A

A[,,i] = i*R;

对于所有i，范围从1到360？

Answer 1

一些基本的乘法和重塑怎么样

set.seed(15) #for reproducibility
R <- matrix(rexp(9, rate=.1), ncol=3);
R
#           [,1]      [,2]      [,3]
# [1,]  2.042281  1.760375 2.9230182
# [2,] 19.466458  6.628580 0.1818078
# [3,]  2.544348 27.541514 4.1325714

dd <- array(sapply(1:360, `*`, R), dim=c(dim(R), 360))
dd[,,1]
#           [,1]      [,2]      [,3]
# [1,]  2.042281  1.760375 2.9230182
# [2,] 19.466458  6.628580 0.1818078
# [3,]  2.544348 27.541514 4.1325714
dd[,,2]
#           [,1]      [,2]      [,3]
# [1,]  4.084562  3.520749 5.8460364
# [2,] 38.932916 13.257161 0.3636157
# [3,]  5.088697 55.083027 8.2651427
dd[,,10]
#           [,1]      [,2]      [,3]
# [1,]  20.42281  17.60375 29.230182
# [2,] 194.66458  66.28580  1.818078
# [3,]  25.44348 275.41514 41.325714

将一个矩阵与一组标量相乘

1 个答案: