[英]R: matrix by vector multiplication
I have following problem: 我有以下问题:
myvec <- c(1:3)
mymat <- as.matrix(cbind(a = 6:15, b = 16:25, c= 26:35))
mymat
a b c
[1,] 6 16 26
[2,] 7 17 27
[3,] 8 18 28
[4,] 9 19 29
[5,] 10 20 30
[6,] 11 21 31
[7,] 12 22 32
[8,] 13 23 33
[9,] 14 24 34
[10,] 15 25 35
I want to multiply the mymat with myvec and construct new vector such that 我想将mymat与myvec相乘并构造新的向量,使得
sum(6*1, 16*2, 26*3)
sum(7*1, 17*2, 27*3)
....................
sum(15*1, 25*2, 35*3)
Sorry, this is simple question that I do not know... 抱歉,这是一个我不知道的简单问题...
Edit: typo corrected 编辑:错别字更正
The %*%
operator in R does matrix multiplication: R中的
%*%
运算符会做矩阵乘法:
> mymat %*% myvec
[,1]
[1,] 116
[2,] 122
...
[10,] 170
An alternative, but longer way can be this one: 另一种方法,但是更长的方法可以是:
rowSums(t(apply(mymat, 1, function(x) myvec*x)),na.rm=T)
Is the only way that I found that can ignore NA's inside the matrix. 是我发现可以忽略矩阵内NA的唯一方法。
Matrices are vectors in column major order: 矩阵是按列主要顺序排列的向量:
colSums( t(mymat) * myvec )
(Edited after hopefully reading question correctly this time.) (希望这次正确阅读问题后进行了编辑。)
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