R 中的分段函数帮助

Question

For a class I must create a piecewise function defined in the following way:

2x-2   , x < -1
0      , -1 <= X <= 1
x^(2)-1, x > 1

I have tried an ifelse sequence but I cant seem to make it work. I've also tried an if, elseif, else sequence, but that only seems to use the first function to calculate answers. The end goal is to have this:

    pwfun(c(-2, 0.5, 3))
    2 0 8

Answer 1

A piece-wise function like below?

pwfun <- function(x) ifelse(x < -1, 2 * x - 2, ifelse(x <= 1, 0, x**2 - 1))

such that

> pwfun(c(-2, 0.5, 3))
[1] -6  0  8

Answer 2

pwfun <- function(x) ifelse(x < -1, (x * x) -2, ifelse(x <= 1, 0, x**2 - 1))


> pwfun(c(-2, 0.5, 3))
[1] -2  0  8

The above edit to ThomasIsCoding's answer gives you what you want, but I would use this approach because it communicates it's intent better:

library(dplyr)

df <- data.frame(x = c(-2, 0.5, 3))

pwfunc <- function(data){
    data %>%
        mutate(y = 
            case_when(x < -1 ~ -2,
                      x > 0 & x <= 1 ~ 0,
                      TRUE ~ x**2 - 1)) ## TRUE in a case_when basically
                                        ## means "everything that isnt caught by my specified conditions
                                        ## becomes..." so it works like the "else" clause
}

Then just call the function on your data:

df <- data.frame(x = c(-2, 0.5, 3))

pwfunc(data)

And get: