我怎样才能将函数应用得狭窄

Question

I make a new function:

  newFunction <- function (varX) {

  lst_a <- c("aa", "bb", "cc")
  lst_b <- c("dd", "ee", "ff")
  lst_c <- c("gg", "hh", "ii")

  ifelse(varX %in% lst_a , x.out <- "List A" , x.out <- "Other List" )
  ifelse(varX %in% lst_b , x.out <- "List B" , x.out )
  ifelse(varX %in%  lst_c , x.out <- "List C" , x.out)

  return(x.out)

 }

When I test the function it works well. But when I apply it to a dataframe it does not work:

     df <- as.data.frame(c("aa","cc","kk", "nn"))
    df$new <- newFunction((df[,1]))

I expected to get "List A", "List A", "Other list", "Other List" - but no such luck have I, and left with me is "Other list", "Other List", "Other list", "Other List"

Answer 1

You could try either

sapply (df[,1], newFunction)

or

map(df[,1], newFunction)

Answer 2

Do it like this:

newFunction <- function (varX) {
   lst_a <- c("aa", "bb", "cc")
   lst_b <- c("dd", "ee", "ff")
   lst_c <- c("gg", "hh", "ii")

   x.out = ifelse(varX %in% lst_a , "List A" , 
             ifelse(varX %in% lst_b , "List B",
               ifelse(varX %in%  lst_c , "List C" , "Other List")))    
   return(x.out)    
 }

Now it is vectorized and you can do df$new <- newFunction(df[,1]) and it is much more efficient.

I'd strongly recommend reading this R-FAQ to understand ifelse vs if(){}else{} .