nth: Extract the first, last or nth value from a vector
These are straightforward wrappers around [[. The main
advantage is that you can provide an optional secondary vector that defines
the ordering, and provide a default value to use when the input is shorter
nth(x, n, order_by = NULL, default = default_missing(x))
For nth(), a single integer specifying the position.
Negative integers index from the end (i.e. -1L will return the
last value in the vector).
If a double is supplied, it will be silently truncated.
An optional vector used to determine the order
A default value to use if the position does not exist in
the input. This is guessed by default for base vectors, where a
missing value of the appropriate type is returned, and for lists, where
a NULL is return.
For more complicated objects, you'll need to supply this value.
Make sure it is the same type as x.