How to access the last value in a vector?

Question

Suppose I have a vector that is nested in a dataframe one or two levels. Is there a quick and dirty way to access the last value, without using the length() fu

Answer 1

I just benchmarked these two approaches on data frame with 663,552 rows using the following code:

system.time(
  resultsByLevel$subject <- sapply(resultsByLevel$variable, function(x) {
    s <- strsplit(x, ".", fixed=TRUE)[[1]]
    s[length(s)]
  })
  )

 user  system elapsed 
  3.722   0.000   3.594 

and

system.time(
  resultsByLevel$subject <- sapply(resultsByLevel$variable, function(x) {
    s <- strsplit(x, ".", fixed=TRUE)[[1]]
    tail(s, n=1)
  })
  )

   user  system elapsed 
 28.174   0.000  27.662 

So, assuming you're working with vectors, accessing the length position is significantly faster.