These functions are variants of map() that iterate over two arguments at
a time.
map2(.x, .y, .f, ..., .progress = FALSE)
map2_lgl(.x, .y, .f, ..., .progress = FALSE)
map2_int(.x, .y, .f, ..., .progress = FALSE)
map2_dbl(.x, .y, .f, ..., .progress = FALSE)
map2_chr(.x, .y, .f, ..., .progress = FALSE)
map2_vec(.x, .y, .f, ..., .ptype = NULL, .progress = FALSE)
walk2(.x, .y, .f, ..., .progress = FALSE)A pair of vectors, usually the same length. If not, a vector of length 1 will be recycled to the length of the other.
A function, specified in one of the following ways:
A named function.
An anonymous function, e.g. \(x, y) x + y or function(x, y) x + y.
A formula, e.g. ~ .x + .y. You must use .x to refer to the current
element of x and .y to refer to the current element of y. Only
recommended if you require backward compatibility with older versions
of R.
Additional arguments passed on to the mapped function.
We now generally recommend against using ... to pass additional
(constant) arguments to .f. Instead use a shorthand anonymous function:
This makes it easier to understand which arguments belong to which function and will tend to yield better error messages.
Whether to show a progress bar. Use TRUE to turn on
a basic progress bar, use a string to give it a name, or see
progress_bars for more details.
If NULL, the default, the output type is the common type
of the elements of the result. Otherwise, supply a "prototype" giving
the desired type of output.
The output length is determined by the length of the input. The output names are determined by the input names. The output type is determined by the suffix:
No suffix: a list; .f() can return anything.
_lgl(), _int(), _dbl(), _chr() return a logical, integer, double,
or character vector respectively; .f() must return a compatible atomic
vector of length 1.
_vec() return an atomic or S3 vector, the same type that .f returns.
.f can return pretty much any type of vector, as long as its length 1.
walk() returns the input .x (invisibly). This makes it easy to
use in a pipe. The return value of .f() is ignored.
Any errors thrown by .f will be wrapped in an error with class
purrr_error_indexed.
x <- list(1, 1, 1)
y <- list(10, 20, 30)
map2(x, y, \(x, y) x + y)
#> [[1]]
#> [1] 11
#>
#> [[2]]
#> [1] 21
#>
#> [[3]]
#> [1] 31
#>
# Or just
map2(x, y, `+`)
#> [[1]]
#> [1] 11
#>
#> [[2]]
#> [1] 21
#>
#> [[3]]
#> [1] 31
#>
# Split into pieces, fit model to each piece, then predict
by_cyl <- mtcars |> split(mtcars$cyl)
mods <- by_cyl |> map(\(df) lm(mpg ~ wt, data = df))
map2(mods, by_cyl, predict)
#> $`4`
#> Datsun 710 Merc 240D Merc 230 Fiat 128 Honda Civic
#> 26.47010 21.55719 21.78307 27.14774 30.45125
#> Toyota Corolla Toyota Corona Fiat X1-9 Porsche 914-2 Lotus Europa
#> 29.20890 25.65128 28.64420 27.48656 31.02725
#> Volvo 142E
#> 23.87247
#>
#> $`6`
#> Mazda RX4 Mazda RX4 Wag Hornet 4 Drive Valiant Merc 280
#> 21.12497 20.41604 19.47080 18.78968 18.84528
#> Merc 280C Ferrari Dino
#> 18.84528 20.70795
#>
#> $`8`
#> Hornet Sportabout Duster 360 Merc 450SE Merc 450SL
#> 16.32604 16.04103 14.94481 15.69024
#> Merc 450SLC Cadillac Fleetwood Lincoln Continental Chrysler Imperial
#> 15.58061 12.35773 11.97625 12.14945
#> Dodge Challenger AMC Javelin Camaro Z28 Pontiac Firebird
#> 16.15065 16.33700 15.44907 15.43811
#> Ford Pantera L Maserati Bora
#> 16.91800 16.04103
#>