Question

Suppose we create a data.frame like this:

> hugs_per_day <- rnorm(10)
> hugs_per_day <- as.data.frame(hugs_per_day)
> hugs_per_day
   hugs_per_day
1  -2.500457495
2  -0.204545274
3  -0.955424927
4   0.320184701
5   1.822908001
6  -0.058679520
7  -0.276004919
8   0.175341993
9  -0.137404974
10  0.005096691

And we want to run a function on each day to return a value based on the results, something like this:

nested_ifelse <- function(x){

ifelse (x > 1,     mood <- "happy",
    ifelse(x < 0,  mood <- "sad", 
                   mood <- "same as yesterday" ))

   return(mood)
}

The nested_ifelse() example does what I want and I’m sure sapply() is the correct R function to populate a new column with results from the function, but I just can’t put the two together.

Answer 1

nested_ifelse should be like this:

nested_ifelse <- function(x){
  mood <- ifelse (x > 1,   "happy",
    ifelse(x < 0, "sad", 
    "same as yesterday" ))
  return(mood)
}

or more simply,

nested_ifelse <- function(x)
  ifelse (x > 1,   "happy",
  ifelse(x < 0, "sad", 
  "same as yesterday" ))

and you can use like this:

d$mood2 <- sapply(d$v, nested_ifelse)

but actually you don’t need to call sapply here:

d$mood <- nested_ifelse(d$v)

is enough.

data d should be like this…

d <- data.frame(v=rnorm(10))