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() function? Something ala PERL's $# special var?
So I would like something like:
dat$vec1$vec2[$#]
instead of
dat$vec1$vec2[length(dat$vec1$vec2)]
I use the tail function:
tail(vector, n=1)
The nice thing with tail is that it works on dataframes too, unlike the x[length(x)] idiom.
If you're looking for something as nice as Python's x[-1] notation, I think you're out of luck. The standard idiom is
x[length(x)]
but it's easy enough to write a function to do this:
last <- function(x) { return( x[length(x)] ) }
This missing feature in R annoys me too!
Combining lindelof's and Gregg Lind's ideas:
last <- function(x) { tail(x, n = 1) }
Working at the prompt, I usually omit the n=, i.e. tail(x, 1).
Unlike last from the pastecs package, head and tail (from utils) work not only on vectors but also on data frames etc., and also can return data "without first/last n elements", e.g.
but.last <- function(x) { head(x, n = -1) }
(Note that you have to use head for this, instead of tail.)