Map over multiple inputs simultaneously.
These functions are variants of map() that iterate over multiple arguments
simultaneously. They are parallel in the sense that each input is processed
in parallel with the others, not in the sense of multicore computing. They
share the same notion of "parallel" as base::pmax() and base::pmin().
map2() and walk2() are specialised for the two argument case; pmap()
and pwalk() allow you to provide any number of arguments in a list. Note
that a data frame is a very important special case, in which case pmap()
and pwalk() apply the function .f to each row. map_dfr(), pmap_dfr()
and map2_dfc(), pmap_dfc() return data frames created by row-binding
and column-binding respectively. They require dplyr to be installed.
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_raw(.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_raw(.l, .f, ...) pmap_dfr(.l, .f, ..., .id = NULL) pmap_dfc(.l, .f, ...) pwalk(.l, .f, ...)
.x, .y |
Vectors of the same length. A vector of length 1 will be recycled. |
.f |
A function, formula, or vector (not necessarily atomic). If a function, it is used as is. If a formula, e.g.
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. If a component is not
present, the value of |
... |
Additional arguments passed on to the mapped function. |
.id |
Either a string or Only applies to |
.l |
A list of vectors, such as a data frame. The length of |
Note that arguments to be vectorised over come before .f,
and arguments that are supplied to every call come after .f.
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.
x <- list(1, 1, 1)
y <- list(10, 20, 30)
z <- list(100, 200, 300)
map2(x, y, ~ .x + .y)
# Or just
map2(x, y, `+`)
pmap(list(x, y, z), sum)
# Matching arguments by position
pmap(list(x, y, z), function(first, second, third) (first + third) * second)
# Matching arguments by name
l <- list(a = x, b = y, c = z)
pmap(l, function(c, b, a) (a + c) * b)
# Split into pieces, fit model to each piece, then predict
by_cyl <- mtcars %>% split(.$cyl)
mods <- by_cyl %>% map(~ lm(mpg ~ wt, data = .))
map2(mods, by_cyl, predict)
# Vectorizing a function over multiple arguments
df <- data.frame(
x = c("apple", "banana", "cherry"),
pattern = c("p", "n", "h"),
replacement = c("P", "N", "H"),
stringsAsFactors = FALSE
)
pmap(df, gsub)
pmap_chr(df, gsub)
# Use `...` to absorb unused components of input list .l
df <- data.frame(
x = 1:3,
y = 10:12,
z = letters[1:3]
)
plus <- function(x, y) x + y
## Not run:
# this won't work
pmap(df, plus)
## End(Not run)
# but this will
plus2 <- function(x, y, ...) x + y
pmap_dbl(df, plus2)
# The "p" for "parallel" in pmap() is the same as in base::pmin()
# and base::pmax()
df <- data.frame(
x = c(1, 2, 5),
y = c(5, 4, 8)
)
# all produce the same result
pmin(df$x, df$y)
map2_dbl(df$x, df$y, min)
pmap_dbl(df, min)
# If you want to bind the results of your function rowwise, use:
# map2_dfr() or pmap_dfr()
ex_fun <- function(arg1, arg2){
col <- arg1 + arg2
x <- as.data.frame(col)
}
arg1 <- 1:4
arg2 <- 10:13
map2_dfr(arg1, arg2, ex_fun)
# If instead you want to bind by columns, use map2_dfc() or pmap_dfc()
map2_dfc(arg1, arg2, ex_fun)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.