在 r 中构建立方根函数，返回负数和正数

Question

I'm trying to build a cubic root function that returns this output:

cr(27)

output:

3

cr(-27) 

output:

-3

I tried the following:

cr<- function(x){
  if(x < 0 & x> 0 & x== 0){
    cat("Error, not possible ")
  }
  else{
    cat((x^(1/3)))
    cat(" ")
  } 
}

I'm getting error for -27:

Nan

Answer 1

R is giving you one of the cube roots. The one it's giving you happens to be complex.

x <- -27

as.complex(x)^(1 / 3)
#> [1] 1.5+2.598076i

If you want the real root, calculate it like this.

sign(x) * abs(x)^(1 / 3)
#> [1] -3