r - 使用 `.value` 和 `pivot_longer()` 时如何将后缀附加到 `names_pattern`

Question

我想用 pivot_longer()来自 {tidyr} 与 names_pattern将我的数据转换为长格式 而 保留列名中模式匹配之一的前缀字符串。
这似乎违反直觉，但我想在应用数据字典清理步骤之前转换为长格式，这需要原始列名。
设置

library(dplyr)
library(tidyr)

d <- tibble(id = 1,
            other_var = "foo",
            suffix_t1_value1 = "a",
            suffix_t1_value2 = "b",
            suffix_t2_value1 = "c",
            suffix_t2_value2 = "d") 

我所做的

> pivot_longer(d,
               starts_with("suffix"),
               names_pattern = "suffix_t(1|2)_(.*)",
               names_to = c("rep", ".value"))

# A tibble: 2 x 5
     id other_var rep   value1 value2
  <dbl> <chr>     <chr> <chr>  <chr> 
1     1 foo       1     a      b     
2     1 foo       2     c      d    

期望输出

# A tibble: 2 x 5
     id other_var rep   suffix_t1_value1 suffix_t1_value2
  <dbl> <chr>     <chr> <chr>            <chr>           
1     1 foo       1     a                b               
2     1 foo       2     c                d               

我试过的
尝试 1

> pivot_longer(d,
               starts_with("suffix"),
               names_pattern = "suffix_t(1|2)_(.*)",
               names_to = c("rep", "suffix_t1_{.value}"))

尝试 2

> pivot_longer(d,
               starts_with("suffix"),
               names_pattern = "suffix_t(1|2)_(.*)",
               names_to = c("rep", paste0("suffix_t1_", ".value")))

Answer 1

我假设您想在 pivot_longer 中一步完成。 .我还没有弄清楚，如果可能的话，但如果两步过程没问题，那么下面的方法应该可行:

library(dplyr)
library(tidyr)

d %>% pivot_longer(starts_with("suffix"),
                   names_pattern = "suffix_t(1|2)_(.*)",
                   names_to = c("rep", ".value")
             ) %>% 
  rename_with(~ gsub("(.*)", "suffix_t1_\\1", .x),
              starts_with("value"))

#> # A tibble: 2 x 5
#>      id other_var rep   suffix_t1_value1 suffix_t1_value2
#>   <dbl> <chr>     <chr> <chr>            <chr>           
#> 1     1 foo       1     a                b               
#> 2     1 foo       2     c                d

创建于 2021-06-09 由 reprex package (v0.3.0)

更新
深入挖掘后 pivot_longer有点，我不认为可以访问 .value内 paste以及粘合语法 {.value}好像不支持。
但是，{tidyr} 提供了使用 build_longer_spec 进行旋转的构建块。这允许我们创建自己的 my_pivot_longer我们可以在其中包含 names_fn 的函数将一个函数应用于新列名的参数，在这里我们可以使用 gsub添加前缀或后缀。

my_pivot_longer <- function(data,
                            cols,
                            names_to = "name",
                            names_pattern = NULL,
                            names_fn = NULL) {
  
  spec <- build_longer_spec(data,
                            cols,
                            names_pattern = names_pattern,
                            names_to = names_to)

  if (!is.null(names_fn)) {
    fn <- rlang::as_function(names_fn)
    spec$.value <-  fn(spec$.value)
  }
  
  pivot_longer_spec(data, spec)
    
}

d %>% 
  my_pivot_longer(starts_with("suffix"),
                  names_pattern = "suffix_t(1|2)_(.*)",
                  names_to = c("rep", ".value"),
                  names_fn = ~ gsub("(.*)", "suffix_t1_\\1", .x))
#> Note: Using an external vector in selections is ambiguous.
#> ℹ Use `all_of(cols)` instead of `cols` to silence this message.
#> ℹ See <https://tidyselect.r-lib.org/reference/faq-external-vector.html>.

#> This message is displayed once per session.
#> # A tibble: 2 x 5
#>      id other_var rep   suffix_t1_value1 suffix_t1_value2
#>   <dbl> <chr>     <chr> <chr>            <chr>           
#> 1     1 foo       1     a                b               
#> 2     1 foo       2     c                d

创建于 2021-06-09 由 reprex package (v0.3.0)