Glue 列规范中的“fn”和“col”arguments 在哪里命名 dplyr 中的列（使用 `across` 和 `where` 来自哪里？

Question

I was going through the vignette ( https://cran.r-project.org/web/packages/dplyr/vignettes/colwise.html ) for column-wise options in dplyr and I came across this: (copied verbatim from the vignette)

---

Control how the names are created with the.names argument which takes a glue spec:

starwars %>% summarise(across(where(is.numeric), min_max, .names = "{fn}.{col}"))
#> # A tibble: 1 x 6
#>   min.height max.height min.mass max.mass min.birth_year max.birth_year
#>        <int>      <int>    <dbl>    <dbl>          <dbl>          <dbl>
#> 1         66        264       15     1358              8            896

---

My question is: where did the variables fn and col come from? I don't see anything about that on the main Glue vignette. The corresponding arguments to across are .fns and .cols so I don't see the exact correspondence. This seems like too obscure an issue for me to be going on a wild goose chase through the documentation so I was hoping that someone could point me in the right direction.

Answer 1

From the online help for across :

.names
A glue specification that describes how to name the output columns. This can use {col} to stand for the selected column name, and {fn} to stand for the name of the function being applied. The default ( NULL ) is equivalent to {col} for the single function case and {col}_{fn} for the case where a list is used for .fns .