How do you use reference a variable from a list in a for loop in R?-CodePudding

I'm trying to write some code to iterate through a list of categorical variables and run some summary statistics on each, but am having trouble getting the variable to be recognized in the for loop. It's trying to group by the dummy name of the for loop ('var', in following example), rather than what it's referencing. Simple example below.

library(dplyr)
cat_vars <- c('hair_color', 'skin_color', 'eye_color')
for (var in cat_vars){
   starwars %>%
      group_by(var) %>%
      summarise(n())
}

Thanks for the help!

CodePudding user response：

To refer to variable names stored as character, use the .data pronoun, like this: .data[[var]].

As written, your for loop won't modify your data or produce any output. What do you want it to do? To print results of each loop, add print():

for (var in cat_vars){
  starwars %>%
    group_by(.data[[var]]) %>%
    summarise(n()) %>% 
    print()
}

#> # A tibble: 13 x 2
#>    hair_color    `n()`
#>    <chr>         <int>
#>  1 auburn            1
#>  2 auburn, grey      1
#>  3 auburn, white     1
#>  4 black            13
#>  5 blond             3
#>  6 blonde            1
#>  7 brown            18
#>  8 brown, grey       1
#>  9 grey              1
#> 10 none             37
#> 11 unknown           1
#> 12 white             4
#> 13 <NA>              5
#> 
#> # A tibble: 31 x 2
#>    skin_color          `n()`
#>    <chr>               <int>
#>  1 blue                    2
#>  2 blue, grey              2
#>  3 brown                   4
#>  4 brown mottle            1
#>  5 brown, white            1
#>  6 dark                    6
#>  7 fair                   17
#>  8 fair, green, yellow     1
#>  9 gold                    1
#> 10 green                   6
#> # ... with 21 more rows
#> 
#> # A tibble: 15 x 2
#>    eye_color     `n()`
#>    <chr>         <int>
#>  1 black            10
#>  2 blue             19
#>  3 blue-gray         1
#>  4 brown            21
#>  5 dark              1
#>  6 gold              1
#>  7 green, yellow     1
#>  8 hazel             3
#>  9 orange            8
#> 10 pink              1
#> 11 red               5
#> 12 red, blue         1
#> 13 unknown           3
#> 14 white             1
#> 15 yellow           11

^{Created on 2022-03-17 by the reprex package (v2.0.1)}