问题描述
我想对这个函数进行编程,以便指定列名的参数尽可能灵活。因此,我决定使用 dot-dot-dot (...
)。
但是,我不知道如何合并tidyselect
的选择助手(即contains
、starts_with
等)
示例
举个例子,假设我想为 dplyr::coalesce()
编写一个包装器。
library(rlang)
library(dplyr)
my_coalesce_func <- function(dat,...) {
# step 1: save `...` into cols (https://tidyeval.tidyverse.org/multiple.html)
cols <- enquos(...)
# step 2: mutate new column `new_col` that coalesces columns of interest
mutate(dat,new_col = coalesce(!!!cols))
}
# toy data
my_df <-
data.frame(
col_a = c(2,2,5,3),col_b = c(NA,4,3,1),col_c = c(4,1,2),col_d = c(1,NA,4),col_e = c(3,5),extra_col = 1:5
)
# run the function -- works fine when we explicitly provide column names
my_coalesce_func(dat = my_df,col_a,col_b,col_c,col_d,col_e)
#> col_a col_b col_c col_d col_e extra_col new_col
#> 1 2 NA 4 1 3 1 2
#> 2 2 4 5 NA 3 2 2
#> 3 5 2 3 4 1 3 5
#> 4 5 3 1 2 4 4 5
#> 5 3 1 2 4 5 5 3
# run the function -- fails to use a select helper
my_coalesce_func(dat = my_df,starts_with("col"))
#> Error: Problem with `mutate()` column `new_col`.
#> i `new_col = coalesce(starts_with("col"))`.
#> x `starts_with()` must be used within a *selecting* function.
#> i See <https://tidyselect.r-lib.org/reference/faq-selection-context.html>.
由 reprex package (v2.0.0) 于 2021 年 7 月 1 日创建
我需要向 my_coalesce_func()
添加什么才能成功运行
my_coalesce_func(dat = my_df,starts_with("col"))
或任何其他传递给 ...
的选择助手。
谢谢!
解决方法
基于这个answer,一个技巧是依赖dplyr::select()
:
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter,lag
#> The following objects are masked from 'package:base':
#>
#> intersect,setdiff,setequal,union
my_coalesce_func = function(data,...) {
data %>%
select(...) %>%
transmute(new_col = coalesce(!!!.)) %>%
bind_cols(data,.)
}
my_df <-
data.frame(
col_a = c(2,2,5,3),col_b = c(NA,4,3,1),col_c = c(4,1,2),col_d = c(1,NA,4),col_e = c(3,5),extra_col = 1:5
)
# explicitly provide column names
my_coalesce_func(dat = my_df,col_d,col_e)
#> col_a col_b col_c col_d col_e extra_col new_col
#> 1 2 NA 4 1 3 1 1
#> 2 2 4 5 NA 3 2 3
#> 3 5 2 3 4 1 3 4
#> 4 5 3 1 2 4 4 2
#> 5 3 1 2 4 5 5 4
# use tidyselect helpers
my_coalesce_func(dat = my_df,starts_with("col"),-(col_a:col_c))
#> col_a col_b col_c col_d col_e extra_col new_col
#> 1 2 NA 4 1 3 1 1
#> 2 2 4 5 NA 3 2 3
#> 3 5 2 3 4 1 3 4
#> 4 5 3 1 2 4 4 2
#> 5 3 1 2 4 5 5 4
由 reprex package (v1.0.0) 于 2021 年 7 月 1 日创建