list2env.r

## list2env() example
##
## An occasionally useful fn to turn list elements into objects. You usually
## want to keep your dfs etc as some kind of list, because it's much neater,
## but sometimes you want to spit out a bunch of named objects.

## Base R version
## We need to take care not to mislabel the list elements, e.g. by mistakenly
## assuming things about the correspondence between elements and names.
## To see why this is bad try e.g. unique(mtcars$cyl), which will be in
## the "wrong" order if you wanted to use it to name the list elements from
## split(). So we write an anonymous function to name things inline.
mtcars |>
  split(mtcars$cyl) |>                       # Convert to list of three dfs.
  (\(x) setNames(x, paste0("cyl",            # Name the elements cyl4, cyl6,
                           names(x))))() |>  # cyl8, using an anonymous fn.
  list2env(envir = .GlobalEnv)               # Turn them into objects.
#> <environment: R_GlobalEnv>

## Now e.g this exists
cyl4
#>                 mpg cyl  disp  hp drat    wt  qsec vs am gear carb
#> Datsun 710     22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
#> Merc 240D      24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
#> Merc 230       22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
#> Fiat 128       32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
#> Honda Civic    30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
#> Toyota Corolla 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
#> Toyota Corona  21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
#> Fiat X1-9      27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
#> Porsche 914-2  26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
#> Lotus Europa   30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
#> Volvo 142E     21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2

## Delete
rm(list= c("cyl4", "cyl6", "cyl8"))

## Tidyverse version
## Again naming the list is the point where it's easy to make an error.
## This is why group_split refuses to return named lists, btw. But we can
## do something similar with map_chr() to get past this. OTOH the fact
## it's kinda awkward is informative! NB use of magrittr pipe here.
library(tidyverse)
mtcars %>%
  group_split(cyl) %>%
  set_names(map_chr(., ~ paste0("cyl", .x$cyl[1]))) %>%
  list2env(envir = .GlobalEnv)
#> <environment: R_GlobalEnv>

## Now e.g this exists again
cyl6
#> # A tibble: 7 × 11
#>     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1  21       6  160    110  3.9   2.62  16.5     0     1     4     4
#> 2  21       6  160    110  3.9   2.88  17.0     0     1     4     4
#> 3  21.4     6  258    110  3.08  3.22  19.4     1     0     3     1
#> 4  18.1     6  225    105  2.76  3.46  20.2     1     0     3     1
#> 5  19.2     6  168.   123  3.92  3.44  18.3     1     0     4     4
#> 6  17.8     6  168.   123  3.92  3.44  18.9     1     0     4     4
#> 7  19.7     6  145    175  3.62  2.77  15.5     0     1     5     6