purrr (version 0.2.3)

map2: Map over multiple inputs simultaneously.

Description

These functions are variants of map() iterate over multiple arguments in parallel. map2() and walk2() are specialised for the two argument case; pmap() and pwalk() allow you to provide any number of arguments in a list.

Usage

map2(.x, .y, .f, ...)
map2_lgl(.x, .y, .f, ...)
map2_int(.x, .y, .f, ...)
map2_dbl(.x, .y, .f, ...)
map2_chr(.x, .y, .f, ...)
map2_dfr(.x, .y, .f, ..., .id = NULL)
map2_dfc(.x, .y, .f, ...)
walk2(.x, .y, .f, ...)
pmap(.l, .f, ...)
pmap_lgl(.l, .f, ...)
pmap_int(.l, .f, ...)
pmap_dbl(.l, .f, ...)
pmap_chr(.l, .f, ...)
pmap_dfr(.l, .f, ..., .id = NULL)
pmap_dfc(.l, .f, ...)
pwalk(.l, .f, ...)

Arguments

.x, .y

Vectors of the same length. A vector of length 1 will be recycled.

.f

A function, formula, or atomic vector.

If a function, it is used as is.

If a formula, e.g. ~ .x + 2, it is converted to a function. There are three ways to refer to the arguments:

• For a single argument function, use .

• For a two argument function, use .x and .y

• For more arguments, use ..1, ..2, ..3 etc

This syntax allows you to create very compact anonymous functions.

If character vector, numeric vector, or list, it is converted to an extractor function. Character vectors index by name and numeric vectors index by position; use a list to index by position and name at different levels. Within a list, wrap strings in get_attr() to extract named attributes. If a component is not present, the value of .default will be returned.

...

Additional arguments passed on to .f.

.id

If not NULL a variable with this name will be created giving either the name or the index of the data frame.

.l

A list of lists. The length of .l determines the number of arguments that .f will be called with. List names will be used if present.

Value

An atomic vector, list, or data frame, depending on the suffix. Atomic vectors and lists will be named if .x or the first element of .l is named.

If all input is length 0, the output will be length 0. If any input is length 1, it will be recycled to the length of the longest.

Details

Note that arguments to be vectorised over come before the .f, and arguments that are supplied to every call come after .f.

See Also

Other map variants: imap, invoke, lmap, map, modify

Examples

# NOT RUN {
x <- list(1, 10, 100)
y <- list(1, 2, 3)
z <- list(5, 50, 500)

map2(x, y, ~ .x + .y)
# Or just
map2(x, y, `+`)

# Split into pieces, fit model to each piece, then predict
by_cyl <- mtcars %>% split(.$cyl)
mods <- by_cyl %>% map(~ lm(mpg ~ wt, data = .))
map2(mods, by_cyl, predict)

pmap(list(x, y, z), sum)

# Matching arguments by position
pmap(list(x, y, z), function(a, b ,c) a / (b + c))

# Matching arguments by name
l <- list(a = x, b = y, c = z)
pmap(l, function(c, b, a) a / (b + c))

# Vectorizing a function over multiple arguments
df <- data.frame(
  x = c("apple", "banana", "cherry"),
  pattern = c("p", "n", "h"),
  replacement = c("x", "f", "q"),
  stringsAsFactors = FALSE
  )
pmap(df, gsub)
pmap_chr(df, gsub)

## Use `...` to absorb unused components of input list .l
df <- data.frame(
  x = 1:3 + 0.1,
  y = 3:1 - 0.1,
  z = letters[1:3]
)
plus <- function(x, y) x + y
# }
# NOT RUN {
## this won't work
pmap(df, plus)
# }
# NOT RUN {
## but this will
plus2 <- function(x, y, ...) x + y
pmap_dbl(df, plus2)

# }