Shortcut for if else

Question

What is the shortest way to express the folowing decission rule

df<-data.frame(a=LETTERS[1:5],b=1:5)
index<-df[,"a"]=="F"
if(any(index)){
  df$new<-"A"
}else{
  df$new<-"B"
}

Answer 1

Shortest is

df$new=c("B","A")[1+any(df$a=="F")]

More elegant is:

df$new <- if (any(df$a == "F")) "A" else "B"

or

df <- transform(df, new = if (any(a == "F")) "A" else "B")

The ifelse operator was suggested twice, but I would reserve it for a different type of operation:

df$new <- ifelse(df$a == "F", "A", "B")

would put a A or a B on every row depending on the value of a in that row only (which is not what your code is currently doing.)

Answer 2

Maybe using the vectorized version ifelse

> df$new <- ifelse(any(df[,"a"]=="F"), "A", "B")
> df
  a b new
1 A 1   B
2 B 2   B
3 C 3   B
4 D 4   B
5 E 5   B