在R中动态创建和评估函数

如何解决在R中动态创建和评估函数

我正在尝试从字符串输入中动态创建和评估函数，并再次陷入元编程/评估（https://adv-r.hadley.nz/metaprogramming.html）的困境。我觉得这已经得到了解答，但是我进行了搜索，但无法通过其他帖子找出解决方案。但是，如果已有答案，请告诉我并标记为重复。非常感谢您的时间和帮助！下面是该问题的代表。

library(dplyr)
library(purrr)
library(rlang)
library(palmerpenguins)

# Create data to join with penguins
penguin_colors <-
  tibble(
    species = c("Adelie","Chinstrap","Gentoo"),color = c("orange","purple","green")
)

# Create function to do specified join and print join type
foo <- function(JOINTYPE) {
  
  # DOESN'T RUN
  # JOINTYPE_join(penguins,penguin_colors,by = "species")
  # call2(sym(paste0(JOINTYPE,"_join")),x = penguins,y = penguin_colors,by = "species")
  
  print(JOINTYPE)
}

# Desired behavior of foo when JOINTYPE == "inner"
inner_join(penguins,by = "species")
#> # A tibble: 344 x 9
#>    species island bill_length_mm bill_depth_mm flipper_length_… body_mass_g
#>    <chr>   <fct>           <dbl>         <dbl>            <int>       <int>
#>  1 Adelie  Torge…           39.1          18.7              181        3750
#>  2 Adelie  Torge…           39.5          17.4              186        3800
#>  3 Adelie  Torge…           40.3          18                195        3250
#>  4 Adelie  Torge…           NA            NA                 NA          NA
#>  5 Adelie  Torge…           36.7          19.3              193        3450
#>  6 Adelie  Torge…           39.3          20.6              190        3650
#>  7 Adelie  Torge…           38.9          17.8              181        3625
#>  8 Adelie  Torge…           39.2          19.6              195        4675
#>  9 Adelie  Torge…           34.1          18.1              193        3475
#> 10 Adelie  Torge…           42            20.2              190        4250
#> # … with 334 more rows,and 3 more variables: sex <fct>,year <int>,#> #   color <chr>
print("inner")
#> [1] "inner"

# Use function in for loop
for (JOINTYPE in c("inner","left","right")) {
  foo(JOINTYPE)
}
#> [1] "inner"
#> [1] "left"
#> [1] "right"

# Use function in vectorised fashion
walk(c("inner","right"),foo)
#> [1] "inner"
#> [1] "left"
#> [1] "right"

^{由reprex package（v0.3.0）于2020-10-27创建}

解决方法

一种选择是使用get()来检索适当的功能：

join <- function(JOINTYPE) {
    get( paste0(JOINTYPE,"_join") )
}

join("inner")(penguins,penguin_colors,by="species")

如果使用rlang，则此处更合适的功能是rlang::exec：

join2 <- function(JOINTYPE,...) {
    rlang::exec( paste0(JOINTYPE,"_join"),... )
}

join2("inner",penguins,by="species")