r - 有条件地显示通过 withCallingHandlers 捕获的警告消息

Question

背景
我有一个简单的脚本，它遍历目录中可用的 CSV 文件，并使用 read_csv 将它们读入一个数据框。和 map_dfr分别发挥作用。该脚本可能会遇到缺少列的文件。在那种情况下 read_csv将产生一个警告，因为我通过 cols_only 指定列名，我想保留。
期望的结果
我希望能够在显示可选警告的情况下运行此脚本。我正在尝试使用 withCallingHandlers 捕获此输出然后，根据函数参数的值，显示警告或不执行任何操作并继续。
问题
即使 show_warnings 也不会显示警告是 TRUE .好像是 warning `withCallingHandlers 的元素不被评估。

例子

# Notes
# Conditionally import files and glide over files with missing columns

# Settings ----------------------------------------------------------------

# Libs
library("tidyverse")
library("fs")

# Constants
pth_tmp_files <- path_temp("temp_csvs")
dir_create(pth_tmp_files)

# Files -------------------------------------------------------------------

# Create a set of sample files
while (length(dir_ls(pth_tmp_files)) < 11) {
    write_csv(x = mtcars,
              file = file_temp("sample_csv_", pth_tmp_files, "csv"))
}

# Add one 'damaged' file
write_csv(
    x = subset(mtcars, select = -cyl),
    file = file_temp("broken_sample_csv_", pth_tmp_files, "csv")
)

# Importer ----------------------------------------------------------------

append_files <- function(files_list, show_warnings) {
    csv_reader <- function(import_file, show_warnings = show_warnings) {
        withCallingHandlers(
            suppressWarnings(expr = {
                read_csv(
                    file = import_file,
                    col_types = cols_only(cyl = col_integer(),
                                          am = col_integer())
                )
            }),
            warning = function(w) {
                if (show_warnings) {
                    warning(w, immediate. = TRUE)
                }
            }
        )

    }

    imported_files <- map_dfr(.x = files_list,
                              .f = ~ csv_reader(import_file = .x),
                              .id = "origin_file")

    mutate(imported_files, origin_file = path_ext_remove(path_file(origin_file))) %>%
        arrange(desc(origin_file))
}

# Tests -------------------------------------------------------------------

# Should return data.frame(tibble) object without warnings
append_files(dir_ls(pth_tmp_files), show_warnings = FALSE)
# Correct    

# Should show warnings and return identical object
append_files(dir_ls(pth_tmp_files), show_warnings = TRUE)
# Object returned with no warnings

笔记

我最感兴趣的是正确使用 withCallingHandlers和/或 invokeRestart职能。我不想要使用 tryCatch 的解决方案因为我最感兴趣的是了解其他错误处理方法。

Answer 1

问题是您使用的是 suppressWarnings在您的expr = 内参数，因此您的 withCallingHandlers 无需处理任何警告包装器(实际上 suppressWarnings 已经在内部使用了 withCallingHandlers，所以它也增加了一层冗余。)
关键是如果发出警告消息并且用户请求 show_warnings = FALSE，则使用重启条件“muffleWarning”调用重启。 .
顺便说一句，您需要更改您的 show_warnings 的名称。内部函数中的参数或显式传递外部函数的show_warnings参数到您的map call - 否则 R 无法确定它正在处理的 promise 对象。

append_files <- function(files_list, show_warnings) {
  
    csv_reader <- function(import_file, show_warnings = show_warnings) {
        
      withCallingHandlers(
            expr    = read_csv(file      = import_file,
                               col_types = cols_only(cyl = col_integer(),
                                                     am  = col_integer())),
            warning = function(w) {
                       if(!show_warnings) tryInvokeRestart("muffleWarning")
            }
        )
    }

    imported_files <- map_dfr(.x = files_list,
                              .f = ~ csv_reader(import_file = .x, show_warnings),
                              .id = "origin_file")

    mutate(imported_files, 
           origin_file = path_ext_remove(path_file(origin_file))) %>%
    arrange(desc(origin_file))
}

所以现在我们有:

append_files(dir_ls(pth_tmp_files), show_warnings = FALSE)
#> # A tibble: 384 x 3
#>    origin_file               am   cyl
#>    <chr>                  <int> <int>
#>  1 sample_csv_1950b846938     1     6
#>  2 sample_csv_1950b846938     1     6
#>  3 sample_csv_1950b846938     1     4
#>  4 sample_csv_1950b846938     0     6
#>  5 sample_csv_1950b846938     0     8
#>  6 sample_csv_1950b846938     0     6
#>  7 sample_csv_1950b846938     0     8
#>  8 sample_csv_1950b846938     0     4
#>  9 sample_csv_1950b846938     0     4
#> 10 sample_csv_1950b846938     0     6
#> # ... with 374 more rows

和

append_files(dir_ls(pth_tmp_files), show_warnings = TRUE)
#> # A tibble: 384 x 3
#>    origin_file               am   cyl
#>    <chr>                  <int> <int>
#>  1 sample_csv_1950b846938     1     6
#>  2 sample_csv_1950b846938     1     6
#>  3 sample_csv_1950b846938     1     4
#>  4 sample_csv_1950b846938     0     6
#>  5 sample_csv_1950b846938     0     8
#>  6 sample_csv_1950b846938     0     6
#>  7 sample_csv_1950b846938     0     8
#>  8 sample_csv_1950b846938     0     4
#>  9 sample_csv_1950b846938     0     4
#> 10 sample_csv_1950b846938     0     6
#> # ... with 374 more rows
#> Warning message:
#> The following named parsers don't match the column names: cyl