不断地将许多列相乘以形成一个新变量 [英] continually multiply many columns to form a new variable

问题描述

我最近想连续乘许多列并在R中形成一个新变量.

I recently want to continually multiply many columns and form a new variable in R.

我发现R中有一个 prod 函数，它可以提供许多向量或矩阵中所有元素的乘积.

I found that there is a prod function in R, which could provide the product of all elements in many vectors or matrices.

但是，我不想获得所有元素的乘积.相反，我想获取每一行的乘积.

However, I do not want to get the product of all element. Instead, I want to get the product of each row.

我可以使用带有循环的代码执行以下操作:

I can do it with code with loop as following:

t <-
 data.frame(x1=round(round(runif(10),1)+1),
            x2=round(round(runif(10),1)+1))
for(i in 1:nrow(t)) {    t$y[i] <- prod(t[i,]) }

但是，我想知道是否有更有效的方法或简单的功能，因为我可以像 prod(t $ 1:t $ 2)这样使用并获得所需的结果.

However, I wonder whether there is more efficient way or easy function, in that I can used like prod(t$1:t$2) and get the result I want.

推荐答案

@akrun答案的 base 变体为

The base variant of @akrun's answer would be

x <- matrix(1:20, ncol = 4)

     [,1] [,2] [,3] [,4]
[1,]    1    6   11   16
[2,]    2    7   12   17
[3,]    3    8   13   18
[4,]    4    9   14   19
[5,]    5   10   15   20

apply(x, 1, prod)
[1]  1056  2856  5616  9576 15000

与 matrixStats :: rowProd()相比，它也可以在 data.frame 上使用.

In contrast to matrixStats::rowProd(), this also works on a data.frame.

x <- as.data.frame(matrix(1:20, ncol = 4))
x$new <- apply(x, 1, prod)

> x
  V1 V2 V3 V4   new
1  1  6 11 16  1056
2  2  7 12 17  2856
3  3  8 13 18  5616
4  4  9 14 19  9576
5  5 10 15 20 15000

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