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 than
nth(x, n, order_by = NULL, default = default_missing(x))
first(x, order_by = NULL, default = default_missing(x))
last(x, order_by = NULL, default = default_missing(x))
- A vector
nth_value, a single integer specifying the position. If a numeric 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 atomic vectors, where a missing value of the
appropriate type is return, and for lists, where a
NULLis return. For more complicated objects, you'll need to supply this value.
A single value.
[[ is used to do the subsetting.
x <- 1:10 y <- 10:1 last(x) last(x, y)