Switch

Rather then string together multiple if - else if chains, you can often use switch.

centre <- function(x, type) {
  switch(type,
    mean = mean(x),
    median = median(x),
    trimmed = mean(x, trim = .1),
    stop("Invalid `type` value")
  )
}

Last component should always throw an error, as unmatched inputs would otherwise invisibly return NULL. Book recommends to only use character inputs for switch().

vec <- c(1:20,50:55)
centre(vec, "mean")
#> [1] 20.19231
centre(vec, "median")
#> [1] 13.5
centre(vec, "trimmed")
#> [1] 18.77273

set.seed(123)
x <- rlnorm(100)

centers <- data.frame(type = c('mean', 'median', 'trimmed'))
centers$value = sapply(centers$type, \(t){centre(x,t)})

require(ggplot2)
ggplot(data = data.frame(x), aes(x))+
  geom_density()+
  geom_vline(data = centers, 
             mapping = aes(color = type, xintercept = value), 
             linewidth=0.5,linetype="dashed") +
  xlim(-1,10)+
  theme_bw()

Example from book of “falling through” to next value

legs <- function(x) {
  switch(x,
    cow = ,
    horse = ,
    dog = 4,
    human = ,
    chicken = 2,
    plant = 0,
    stop("Unknown input")
  )
}
legs("cow")
#> [1] 4
#> [1] 4
legs("dog")
#> [1] 4
#> [1] 4