read_delim_chunked functions do not return column specifications

[svraka]

The read_delim functions return the column specification used by readr as an attribute which can be accessed using spec(). However, this is not the case with the read_delim_chunked functions. The specifications are printed but cannot be accessed.

library(readr)
read_csv_chunked(readr_example("mtcars.csv"),
                 callback = ListCallback$new(function(x, pos) spec(x)),
                 chunk_size = 20)
#> 
#> ── Column specification ────────────────────────────────────────────────────────
#> cols(
#>   mpg = col_double(),
#>   cyl = col_double(),
#>   disp = col_double(),
#>   hp = col_double(),
#>   drat = col_double(),
#>   wt = col_double(),
#>   qsec = col_double(),
#>   vs = col_double(),
#>   am = col_double(),
#>   gear = col_double(),
#>   carb = col_double()
#> )
#> [[1]]
#> NULL
#> 
#> [[2]]
#> NULL

Long specifications are truncated by default, thus workarounds, like options(readr.num_columns = Inf) are needed to obtain the full spec. Meanwhile other attributes, like problems can be accessed:

read_csv_chunked(readr_example("mtcars.csv"),
                 callback = ListCallback$new(function(x, pos) problems(x)),
                 chunk_size = 20,
                 col_types = paste0(rep("i", 11), collapse = ""))
#> [[1]]
#> # A tibble: 85 x 4
#>      row   col expected               actual
#>    <int> <int> <chr>                  <chr> 
#>  1     1     5 no trailing characters 3.9   
#>  2     1     6 no trailing characters 2.62  
#>  3     1     7 no trailing characters 16.46 
#>  4     2     5 no trailing characters 3.9   
#>  5     2     6 no trailing characters 2.875 
#>  6     2     7 no trailing characters 17.02 
#>  7     3     1 no trailing characters 22.8  
#>  8     3     5 no trailing characters 3.85  
#>  9     3     6 no trailing characters 2.32  
#> 10     3     7 no trailing characters 18.61 
#> # … with 75 more rows
#> 
#> [[2]]
#> # A tibble: 49 x 4
#>      row   col expected               actual
#>    <int> <int> <chr>                  <chr> 
#>  1    21     1 no trailing characters 21.5  
#>  2    21     3 no trailing characters 120.1 
#>  3    21     5 no trailing characters 3.7   
#>  4    21     6 no trailing characters 2.465 
#>  5    21     7 no trailing characters 20.01 
#>  6    22     1 no trailing characters 15.5  
#>  7    22     5 no trailing characters 2.76  
#>  8    22     6 no trailing characters 3.52  
#>  9    22     7 no trailing characters 16.87 
#> 10    23     1 no trailing characters 15.2  
#> # … with 39 more rows

Chunks have a spec_tbl_df class, which suggests to me that maybe the col spec should also be accessible?

read_csv_chunked(readr_example("mtcars.csv"),
                 callback = ListCallback$new(function(x, pos) class(x)),
                 chunk_size = 20)
#> 
#> ── Column specification ────────────────────────────────────────────────────────
#> cols(
#>   mpg = col_double(),
#>   cyl = col_double(),
#>   disp = col_double(),
#>   hp = col_double(),
#>   drat = col_double(),
#>   wt = col_double(),
#>   qsec = col_double(),
#>   vs = col_double(),
#>   am = col_double(),
#>   gear = col_double(),
#>   carb = col_double()
#> )
#> [[1]]
#> [1] "spec_tbl_df" "tbl_df"      "tbl"         "data.frame" 
#> 
#> [[2]]
#> [1] "spec_tbl_df" "tbl_df"      "tbl"         "data.frame"

^{Created on 2020-11-02 by the reprex package (v0.3.0)}

Session info

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