Map over two inputs

These functions are variants of map() that iterate over two arguments at a time.

Usage

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)

Arguments

.x, .y

A pair of vectors, usually the same length. If not, a vector of length 1 will be recycled to the length of the other.

.f

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:

# Instead of
x |> map(f, 1, 2, collapse = ",")
# do:
x |> map(\(x) f(x, 1, 2, collapse = ","))

This makes it easier to understand which arguments belong to which function and will tend to yield better error messages.

.progress

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.

.ptype

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.

Value

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.

Examples

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 
#>       26.47010       21.55719       21.78307       27.14774 
#>    Honda Civic Toyota Corolla  Toyota Corona      Fiat X1-9 
#>       30.45125       29.20890       25.65128       28.64420 
#>  Porsche 914-2   Lotus Europa     Volvo 142E 
#>       27.48656       31.02725       23.87247 
#> 
#> $`6`
#>      Mazda RX4  Mazda RX4 Wag Hornet 4 Drive        Valiant 
#>       21.12497       20.41604       19.47080       18.78968 
#>       Merc 280      Merc 280C   Ferrari Dino 
#>       18.84528       18.84528       20.70795 
#> 
#> $`8`
#>   Hornet Sportabout          Duster 360          Merc 450SE 
#>            16.32604            16.04103            14.94481 
#>          Merc 450SL         Merc 450SLC  Cadillac Fleetwood 
#>            15.69024            15.58061            12.35773 
#> Lincoln Continental   Chrysler Imperial    Dodge Challenger 
#>            11.97625            12.14945            16.15065 
#>         AMC Javelin          Camaro Z28    Pontiac Firebird 
#>            16.33700            15.44907            15.43811 
#>      Ford Pantera L       Maserati Bora 
#>            16.91800            16.04103 
#>

Usage

Arguments

Value

See also

Examples