detect: Find the value or position of the first match
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detect

R Documentation

Find the value or position of the first match

Description

Find the value or position of the first match

Usage

detect(
  .x,
  .f,
  ...,
  .dir = c("forward", "backward"),
  .right = NULL,
  .default = NULL
)

detect_index(.x, .f, ..., .dir = c("forward", "backward"), .right = NULL)

Arguments

`.x`	A list or vector.
`.f`	A function, specified in one of the following ways: A named function, e.g. `mean`. An anonymous function, e.g. `⁠\(x) x + 1⁠` or `function(x) x + 1`. A formula, e.g. `~ .x + 1`. You must use `.x` to refer to the first argument. Only recommended if you require backward compatibility with older versions of R. A string, integer, or list, e.g. `"idx"`, `1`, or `list("idx", 1)` which are shorthand for `⁠\(x) pluck(x, "idx")⁠`, `⁠\(x) pluck(x, 1)⁠`, and `⁠\(x) pluck(x, "idx", 1)⁠` respectively. Optionally supply `.default` to set a default value if the indexed element is `NULL` or does not exist.
`...`	Additional arguments passed on to `.p`.
`.dir`	If `"forward"`, the default, starts at the beginning of the vector and move towards the end; if `"backward"`, starts at the end of the vector and moves towards the beginning.
`.right`	Please use `.dir` instead.
`.default`	The value returned when nothing is detected.

Value

detect the value of the first item that matches the predicate; detect_index the position of the matching item. If not found, detect returns NULL and detect_index returns 0.

Examples

is_even <- function(x) x %% 2 == 0

3:10 |> detect(is_even)
3:10 |> detect_index(is_even)

3:10 |> detect(is_even, .dir = "backward")
3:10 |> detect_index(is_even, .dir = "backward")


# Since `.f` is passed to as_mapper(), you can supply a
# lambda-formula or a pluck object:
x <- list(
  list(1, foo = FALSE),
  list(2, foo = TRUE),
  list(3, foo = TRUE)
)

detect(x, "foo")
detect_index(x, "foo")


# If you need to find all values, use keep():
keep(x, "foo")

# If you need to find all positions, use map_lgl():
which(map_lgl(x, "foo"))

purrr documentation built on April 3, 2025, 6:13 p.m.