# 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`.x`

as the second argument, and the next value of`.y`

as 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 that`reduce`

returns a correct value when`.x`

is empty. If missing, and`x`

is empty, will throw an error.- .y
For

`reduce2()`

, an additional argument that is passed to`.f`

. If`init`

is not set,`.y`

should 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)
# }
```

*Documentation reproduced from package purrr, version 0.2.3, License: GPL-3 | file LICENSE*