r - 在 dplyr mutate 中，如何使用变量分配新的列名？

Question

我可以在 dplyr mutate 中使用变量来表示列名，只要它在计算部分的右侧即可。这很好用:

library(dplyr)
var <- "mass"
x <- starwars %>%
  mutate(height = height * 2,
         mass = get(var) * 2)

但是，如果我尝试使用变量来表示新的列名称(即在左侧)，它会抛出错误。例如，这会导致错误:

var <- "mass"
x <- starwars %>%
  mutate(height = height * 2,
         get(var) = get(var) * 2)

如何在 mutate 中使用变量作为列名？

Answer 1

在 !! 中使用 := 运算符 - 我们可以使用 [[ 而不是 get使用 .data 代词提取(或转换为 symbol 并求值 (!!)

library(dplyr)
starwars %>%
  mutate(height = height * 2,
         !! var := .data[[var]] * 2)
         #or convert to symbol and evaluate
         # !! var := !! rlang::sym(var) * 2)
         #or use `{{}}`
        # {{var}} := !! rlang::sym(var) * 2)

-输出

# A tibble: 87 × 14
   name               height  mass hair_color    skin_color  eye_color birth_year sex    gender    homeworld species films     vehicles  starships
   <chr>               <dbl> <dbl> <chr>         <chr>       <chr>          <dbl> <chr>  <chr>     <chr>     <chr>   <list>    <list>    <list>   
 1 Luke Skywalker        344   154 blond         fair        blue            19   male   masculine Tatooine  Human   <chr [5]> <chr [2]> <chr [2]>
 2 C-3PO                 334   150 <NA>          gold        yellow         112   none   masculine Tatooine  Droid   <chr [6]> <chr [0]> <chr [0]>
 3 R2-D2                 192    64 <NA>          white, blue red             33   none   masculine Naboo     Droid   <chr [7]> <chr [0]> <chr [0]>
 4 Darth Vader           404   272 none          white       yellow          41.9 male   masculine Tatooine  Human   <chr [4]> <chr [0]> <chr [1]>
 5 Leia Organa           300    98 brown         light       brown           19   female feminine  Alderaan  Human   <chr [5]> <chr [1]> <chr [0]>
 6 Owen Lars             356   240 brown, grey   light       blue            52   male   masculine Tatooine  Human   <chr [3]> <chr [0]> <chr [0]>
 7 Beru Whitesun lars    330   150 brown         light       blue            47   female feminine  Tatooine  Human   <chr [3]> <chr [0]> <chr [0]>
 8 R5-D4                 194    64 <NA>          white, red  red             NA   none   masculine Tatooine  Droid   <chr [1]> <chr [0]> <chr [0]>
 9 Biggs Darklighter     366   168 black         light       brown           24   male   masculine Tatooine  Human   <chr [1]> <chr [0]> <chr [1]>
10 Obi-Wan Kenobi        364   154 auburn, white fair        blue-gray       57   male   masculine Stewjon   Human   <chr [6]> <chr [1]> <chr [5]>
# … with 77 more rows