when
Match/validate a set of conditions for an object and continue with the action associated with the first valid match.
when is a flavour of pattern matching (or an if-else abstraction) in
which a value is matched against a sequence of condition-action sets. When a
valid match/condition is found the action is executed and the result of the
action is returned.
- Keywords
- internal
Usage
when(., ...)Arguments
- .
the value to match against
- ...
formulas; each containing a condition as LHS and an action as RHS. named arguments will define additional values.
Value
The value resulting from the action of the first valid match/condition is returned. If no matches are found, and no default is given, NULL will be returned.
Validity of the conditions are tested with isTRUE, or equivalently
with identical(condition, TRUE).
In other words conditions resulting in more than one logical will never
be valid. Note that the input value is always treated as a single object,
as opposed to the ifelse function.
Examples
# NOT RUN {
1:10 %>%
when(
sum(.) <= 50 ~ sum(.),
sum(.) <= 100 ~ sum(.)/2,
~ 0
)
1:10 %>%
when(
sum(.) <= x ~ sum(.),
sum(.) <= 2*x ~ sum(.)/2,
~ 0,
x = 60
)
iris %>%
subset(Sepal.Length > 10) %>%
when(
nrow(.) > 0 ~ .,
~ iris %>% head(10)
)
iris %>%
head %>%
when(nrow(.) < 10 ~ .,
~ stop("Expected fewer than 10 rows."))
# }