Find head/tail that all satisfies a predicate.

Usage

head_while(.x, .p, ...)

tail_while(.x, .p, ...)

Arguments

.x

A list or atomic vector.

.p

A predicate function specified in one of the following ways:

A named function, e.g. is.character.
An anonymous function, e.g. \(x) all(x < 0) or function(x) all(x < 0).
A logical vector of the same length as .x.
A string, if the elements of .x are themselves lists of objects, giving the name of a logical element in the inner lists.

Only those elements where .p evaluates to TRUE will be kept.

...

Additional arguments passed on to the mapped function.

We now generally recommend against using ... to pass additional (constant) arguments to .f. Instead use a shorthand anonymous function:

# Instead of
x |> map(f, 1, 2, collapse = ",")
# do:
x |> map(\(x) f(x, 1, 2, collapse = ","))

This makes it easier to understand which arguments belong to which function and will tend to yield better error messages.

Value

A vector the same type as .x.

Examples

pos <- function(x) x >= 0
head_while(5:-5, pos)
#> [1] 5 4 3 2 1 0
tail_while(5:-5, negate(pos))
#> [1] -1 -2 -3 -4 -5

big <- function(x) x > 100
head_while(0:10, big)
#> integer(0)
tail_while(0:10, big)
#> integer(0)