`purrr::pmap()` but with `Map()`-like semantics

pMap.R

pMap <- function(.l, .f, ...) {
    .f <- rlang::as_function(.f, ...)
    
    if (rlang::is_named(.l)) {
        fun <- function(...) {
            rlang::fn_env(.f) <- rlang::env(...)
            .f(...)
        }
    } else {
        fun <- .f
    }
    rlang::exec(Map, fun, !!!.l)
}

pMap_dbl <- function(.l, .f, ...) {
    out <- pMap(.l, .f, ...)
    purrr::simplify(out, .type = "double")
}


pMap_dbl(mtcars, max)  # ok
#>  [1] 160.0 160.0 108.0 258.0 360.0 225.0 360.0 146.7 140.8 167.6 167.6 275.8
#> [13] 275.8 275.8 472.0 460.0 440.0  78.7  75.7  71.1 120.1 318.0 304.0 350.0
#> [25] 400.0  79.0 120.3 113.0 351.0 175.0 335.0 121.0

pMap_dbl(mtcars, ~mean(c(...)))  # nice, but same as `pmap_dbl()`
#>  [1] 29.90727 29.98136 23.59818 38.73955 53.66455 35.04909 59.72000 24.63455
#>  [9] 27.23364 31.86000 31.78727 46.43091 46.50000 46.35000 66.23273 66.05855
#> [17] 65.97227 19.44091 17.74227 18.81409 24.88864 47.24091 46.00773 58.75273
#> [25] 57.37955 18.92864 24.77909 24.88027 60.97182 34.50818 63.15545 26.26273

pMap_dbl(mtcars, ~mean(c(mpg, qsec)))  # BUT you can use names as params too!
#>  [1] 18.730 19.010 20.705 20.420 17.860 19.160 15.070 22.200 22.850 18.750
#> [11] 18.350 16.900 17.450 16.600 14.190 14.110 16.060 25.935 24.460 26.900
#> [21] 20.755 16.185 16.250 14.355 18.125 23.100 21.350 23.650 15.150 17.600
#> [31] 14.800 20.000


library(dplyr, warn.conflicts = FALSE)
data('mpg', package = 'ggplot2')

mpg %>% transmute(
    mileage1 = rowMeans(cbind(cty, hwy)),                    # target
    mileage2 = pMap_dbl(lst(cty, hwy), ~mean(c(...))),       # named list, fun uses other param names
    mileage3 = pMap_dbl(lst(cty, hwy), ~mean(c(cty, hwy))),  # named list, fun uses list names as param names
    mileage4 = pMap_dbl(., ~mean(c(cty, hwy))),              # dataframe, fun uses col names as param names
    mileage5 = pMap_dbl(list(cty, hwy), ~mean(c(...)))       # unnamed list, fun uses other param names
)
#> # A tibble: 234 × 5
#>    mileage1 mileage2 mileage3 mileage4 mileage5
#>       <dbl>    <dbl>    <dbl>    <dbl>    <dbl>
#>  1     23.5     23.5     23.5     23.5     23.5
#>  2     25       25       25       25       25  
#>  3     25.5     25.5     25.5     25.5     25.5
#>  4     25.5     25.5     25.5     25.5     25.5
#>  5     21       21       21       21       21  
#>  6     22       22       22       22       22  
#>  7     22.5     22.5     22.5     22.5     22.5
#>  8     22       22       22       22       22  
#>  9     20.5     20.5     20.5     20.5     20.5
#> 10     24       24       24       24       24  
#> # … with 224 more rows