如何简化这个程序? [英] How to simplify this programme?
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问题描述
#f是一个具有两个参数并返回一个值的函数:
f < - 函数(a,b){
a * b
}
#x是a的值组
x < - c(1, 2,3,4)
#y是b的价值组
y< - c(4,5,6)
我想获得f(x,y)的所有可能的值,结果应该是一个矩阵要清楚。现在我正在使用for循环:
m <-c(NULL)
for(a in x) (b,y){
m < - c(m,c(a,b))
}
}
m < - 矩阵(m ,3,4)
但是看起来真的很傻,可以提供一个更简单的方法吗?
谢谢。
解决方案
outer(x,y,f)
#[,1] [,2] [,3]
#[1,] 4 5 6
#[2,] 8 10 12
#[3,] 12 15 18
#[4,] 16 20 24
outer(y,x,f)
#[,1] [,2] [,3] [,4]
#[1,] 4 8 12 16
#[2,] 5 10 15 20
#[3,] 6 12 18 24
The main function is like the following code:
#f is a function that has two parameters and returns one value:
f <- function(a, b) {
a * b
}
#x is a's value group
x <- c(1,2,3,4)
#y is b's value group
y <- c(4,5,6)
I want to get all the possible values of f(x, y), and the result should be a matrix to be clear. Now I am using the for loop:
m <- c(NULL)
for (a in x) {
for (b in y) {
m <- c(m, c(a, b))
}
}
m <- matrix(m, 3, 4)
But it seems really very very silly.Can any one provide a simpler way?
Thank you.
解决方案
outer(x, y, f)
# [,1] [,2] [,3]
#[1,] 4 5 6
#[2,] 8 10 12
#[3,] 12 15 18
#[4,] 16 20 24
outer(y, x, f)
# [,1] [,2] [,3] [,4]
#[1,] 4 8 12 16
#[2,] 5 10 15 20
#[3,] 6 12 18 24
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