使用 embrace {{ arg }} 在 dplyr 中选择负值的问题

Question

我在根据变量选择负数列时遇到问题。我发现这里报告了类似的问题： https://github.com/tidyverse/dplyr/issues/4813 但提供的解决方案不起作用（请参阅下面的 repex）。如果有人知道解决方法，将不胜感激！！这是一个 repex 的问题：

# Load package
library(dplyr, warn.conflicts = F)
ex_data <- tibble(a = 1, b = 2)

# example functions
## Function for checking if target was provided
## else defaults to all numeric columns
check_target <- function(target) {
  target
  target_quoted <- rlang::enquo(target)
  if (rlang::quo_is_null(target_quoted)) {
    rlang::expr(where(is.numeric))
  } else{
    rlang::expr(!!target)
  }
}
## Just soft wrappers to show how the preivews
## function could be used
my_select_embrace <- function(data, target = NULL){
  target <- check_target(target)
  data %>% 
    select({{ target }})
}
my_select_bang <- function(data, target = NULL){
  target <- check_target(target)
  data %>% 
    select(!!target)
}
# Works
ex_data %>% 
  select(-1) %>%
  invisible()
ex_data %>% 
  my_select_bang(tidyselect::vars_select_helpers$where(is.numeric)) %>%
  invisible()
ex_data %>% 
  my_select_bang() %>%
  invisible()
# Fails
ex_data %>% 
  my_select_embrace() %>%
  invisible()
#> Error: object 'is.numeric' not found
ex_data %>% 
  my_select_bang(tidyselect::vars_select_helpers$contains('a')) %>%
  invisible()
#> Error: `contains()` must be used within a *selecting* function.
#> i See <https://tidyselect.r-lib.org/reference/faq-selection-context.html>.
ex_data %>% 
  my_select_embrace(tidyselect::vars_select_helpers$where(is.numeric)) %>%
  invisible()
minus_one <- -1
ex_data %>% 
  my_select_embrace(minus_one)
#> Error: Selections can't have negative values.
ex_data %>% 
  my_select_bang(minus_one)
#> Error: Selections can't have negative values.

^{由 reprex package (v2.0.0)}

于 2021 年 6 月 21 日创建

Answer 1

这是您要找的吗？

library(dplyr, warn.conflicts = F)
ex_data <- tibble(a = 1, b = 2)


my_select_bang <- function(data, target = NULL){
  
  target_quoted <- enquo(target)
  target_null <- rlang::quo_is_null(target_quoted)

  data %>% 
    select(if (target_null) where(is.numeric) else !!target_quoted)
}

# defaults to `where(is.numeric)`
ex_data %>% 
  my_select_bang()
#> # A tibble: 1 x 2
#>       a     b
#>   <dbl> <dbl>
#> 1     1     2

# works with tidyselect syntax as expected
ex_data %>% 
  my_select_bang(contains("a"))
#> # A tibble: 1 x 1
#>       a
#>   <dbl>
#> 1     1

^{由 reprex package (v0.3.0)}

于 2021 年 6 月 21 日创建

如果您不介意在正式函数中使用默认值，那么下面的方法也适用：

my_select_bang <- function(data,
                           target = tidyselect::vars_select_helpers$where(is.numeric)){
  
  data %>% 
    select(!!target)
}

如果您想在矢量中捕获 -1 并在 dplyr::select 或您自己的函数之一中使用它，您应该使用 minus_one <- expr(-1) 捕获它。这样就不会报错了。

minus_one <- expr(-1)

ex_data %>% 
  my_select_bang(minus_one)

#> # A tibble: 1 x 1
#>       b
#>   <dbl>
#> 1     2

^{由 reprex package (v0.3.0)}

于 2021 年 6 月 21 日创建

Answer 2

使原始设计生效的一种方法是在将其发送到 check_target 之前引用 target 并使用 bang-bang (!!) 而不是拥抱 {{ arg }}:

# Load package
library(dplyr, warn.conflicts = F)
ex_data <- tibble(a = 1, b = 2)

# example functions
## Function for checking if target was provided
## else defaults to all numeric columns
check_target <- function(target) {
  if (rlang::quo_is_null(target)) {
    rlang::expr(where(is.numeric))
  } else{
    target
  }
}
## Just soft wrapper to show how the preivews
## function could be used
my_select_bang <- function(data, target = NULL){
  target <- rlang::enquo(target)
  target <- check_target(target)
  data %>% 
    select(!!target)
}
# Works
ex_data %>% 
  select(-1) %>%
  invisible()
ex_data %>% 
  select(contains('a')) %>%
  invisible()
ex_data %>% 
  my_select_bang(where(is.numeric)) %>%
  invisible()
ex_data %>% 
  my_select_bang() %>%
  invisible()
ex_data %>% 
  my_select_bang(contains('a')) %>%
  invisible()
ex_data %>% 
  my_select_bang(-1) %>%
  invisible()

^{由 reprex package (v2.0.0)}

创建于 2021-06-21

使用 embrace {{ arg }} 在 dplyr 中选择负值的问题

Issue with selecting negative values in dplyr with embrace {{ arg }}

r

dplyr

rlang

tidyselect