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 expected.
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))
x |
A vector |
n |
For If a double is supplied, it will be silently truncated. |
order_by |
An optional vector used to determine the order |
default |
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 For more complicated objects, you'll need to supply this value.
Make sure it is the same type as |
A single value. [[ is used to do the subsetting.
x <- 1:10 y <- 10:1 first(x) last(y) nth(x, 1) nth(x, 5) nth(x, -2) nth(x, 11) last(x) # Second argument provides optional ordering last(x, y) # These functions always return a single value first(integer())
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