通过带有“ {{”算子 [英] Tunnel data-variables through env-variable with "{{" operator

问题描述

下面的示例来自 https：// www.tidyverse.org/blog/2020/02/glue-strings-and-tidy-eval/

如何将变量传递给该函数？

How do you pass variables into this function?

library(tidyverse)
#> Warning: package 'tidyverse' was built under R version 3.6.2
#> Warning: package 'tidyr' was built under R version 3.6.2

mean_by <- function(data, by, var, prefix = "avg") {
  data %>%
    group_by({{ by }}) %>%
    summarise("{prefix}_{{ var }}" := mean({{ var }}, na.rm = TRUE))
}

mean_by(mtcars, by = cyl, var = mpg, prefix = "avg")
#> # A tibble: 3 x 2
#>     cyl avg_mpg
#>   <dbl>   <dbl>
#> 1     4    26.7
#> 2     6    19.7
#> 3     8    15.1

# Variables to pass into function
params <-  setdiff(colnames(mtcars) ,"mpg") 

# How do you pass a variables into this function? 
purrr::map(params, mean_by(mtcars, by = .x, var = mpg, prefix = "avg"))
#> Error: Column `.x` is unknown

^{由2020-02-19创建 reprex软件包（v0.3.0）}

^{Created on 2020-02-19 by the reprex package (v0.3.0)}

推荐答案

使用带有列名的 .data 代词：

purrr::map(params, ~ mean_by(mtcars, by = .data[[.x]], var = mpg, prefix = "avg"))

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