reduce
Reduce a list to a single value by iteratively applying a binary function.
reduce() combines from the left, reduce_right() combines from
the right. reduce(list(x1, x2, x3), f) is equivalent to
f(f(x1, x2), x3); reduce_right(list(x1, x2, x3), f) is equivalent to
f(f(x3, x2), x1).
Usage
reduce(.x, .f, ..., .init)reduce_right(.x, .f, ..., .init)
reduce2(.x, .y, .f, ..., .init)
reduce2_right(.x, .y, .f, ..., .init)
Arguments
- .x
A list or atomic vector.
- .f
For
reduce(), a 2-argument function. The function will be passed the accumulated value as the first argument and the "next" value as the second argument.For
reduce2(), a 3-argument function. The function will be passed the accumulated value as the first argument, the next value of.xas the second argument, and the next value of.yas the third argument.- ...
Additional arguments passed on to
.f.- .init
If supplied, will be used as the first value to start the accumulation, rather than using
x[[1]]. This is useful if you want to ensure thatreducereturns a correct value when.xis empty. If missing, andxis empty, will throw an error.- .y
For
reduce2(), an additional argument that is passed to.f. Ifinitis not set,.yshould be 1 element shorter than.x.
Examples
# NOT RUN {
1:3 %>% reduce(`+`)
1:10 %>% reduce(`*`)
paste2 <- function(x, y, sep = ".") paste(x, y, sep = sep)
letters[1:4] %>% reduce(paste2)
letters[1:4] %>% reduce2(c("-", ".", "-"), paste2)
samples <- rerun(2, sample(10, 5))
samples
reduce(samples, union)
reduce(samples, intersect)
x <- list(c(0, 1), c(2, 3), c(4, 5))
x %>% reduce(c)
x %>% reduce_right(c)
# Equivalent to:
x %>% rev() %>% reduce(c)
# }