[ARROW-18219] [R] read_csv_arrow fails when a string contains a backslash-escaped quote mark followed by a comma

• Type: Bug
• Status: Open
• Priority: Critical
• Resolution: Unresolved
• Affects Version/s: 10.0.0
• Component/s: R
• External issue URL: https://github.com/apache/arrow/issues/33405
• Assignee: Unassigned
• Reporter: Danielle Navarro
• Created: 02/Nov/22 05:38
• Updated: 11/Jan/23 11:58

Description

`read_csv_arrow()` incorrectly parses CSV files when a string value contains a comma that appears after a backslash-escaped quote mark. Originally noted by Thomas Klebel https://scicomm.xyz/@tklebel/109270436511066953

This is an example that throws the error:

x <- tempfile()
readr::write_lines(
'
id,text
1,"some text on \\"BLAH
" and X, and Y also"
', x)

cat(system(paste('cat', x), intern = TRUE), sep = "\n")
#> 
#> id,text
#> 1,"some text on \"BLAH\" and X, and Y also"
arrow::read_csv_arrow(x, escape_backslash = TRUE)
#> Error:
#> ! Invalid: CSV parse error: Expected 2 columns, got 3: 1,"some text on \"BLAH\" and X, and Y also"

#> Backtrace:
#> ▆
#> 1. └─arrow (local) `<fn>`(file = x, escape_backslash = TRUE, delim = ",")
#> 2. └─base::tryCatch(...) at r/R/csv.R:217:2
#> 3. └─base (local) tryCatchList(expr, classes, parentenv, handlers)
#> 4. └─base (local) tryCatchOne(expr, names, parentenv, handlers[[1L]])
#> 5. └─value[[3L]](cond)
#> 6. └─arrow:::augment_io_error_msg(e, call, schema = schema) at r/R/csv.R:222:6
#> 7. └─rlang::abort(msg, call = call) at r/R/util.R:251:2

^{Created on 2022-11-02 with [reprex v2.0.2](https://reprex.tidyverse.org)}

This version includes four lines that might potentially error but do not:

x <- tempfile()
readr::write_lines(
'
id,text
2,"some text on X and Y"
3,"some text on X, and Y"
4,"some text on \\"BLAH
"
5,"some text on X and Y, and \\"BLAH
" also"
', x)

cat(system(paste('cat', x), intern = TRUE), sep = "\n")
#> 
#> id,text
#> 2,"some text on X and Y"
#> 3,"some text on X, and Y"
#> 4,"some text on \"BLAH\"
#> 5,"some text on X and Y, and \"BLAH\" also"
arrow::read_csv_arrow(x, escape_backslash = TRUE)
#> # A tibble: 4 × 2
#> id text 
#> <int> <chr> 
#> 1 2 "some text on X and Y" 
#> 2 3 "some text on X, and Y" 
#> 3 4 "some text on \\BLAH\\\"" 
#> 4 5 "some text on X and Y, and \\BLAH\\\" also\""

^{Created on 2022-11-02 with [reprex v2.0.2](https://reprex.tidyverse.org)}

I'm not sure if the problem is R specific. I've partially reproduced the error using reticulate and pyarrow as follows, but notice that this errors at a different point: the pyarrow version appears to fail with the comma preceding the backslash-escaped quote mark:

x <- tempfile()
readr::write_lines(
'
id,text
1,"some text on X and Y"
2,"some text on X, and Y"
3,"some text on \\"BLAH
"
4,"some text on X and Y, and \\"BLAH
" also"
5,"some text on \\"BLAH
" and X, and Y also"
', x)

cat(system(paste('cat', x), intern = TRUE), sep = "\n")
#> 
#> id,text
#> 1,"some text on X and Y"
#> 2,"some text on X, and Y"
#> 3,"some text on \"BLAH\"
#> 4,"some text on X and Y, and \"BLAH\" also"
#> 5,"some text on \"BLAH\" and X, and Y also"

csv <- reticulate::import("pyarrow.csv")
opt <- csv$ParseOptions(escape_char='
')
csv$read_csv(x, parse_options = opt)
#> Error in py_call_impl(callable, dots$args, dots$keywords): pyarrow.lib.ArrowInvalid: CSV parse error: Expected 2 columns, got 3: 3,"some text on \"BLAH\"
#> 4,"some text on X and Y, and \"BLAH\" also"

^{Created on 2022-11-02 with [reprex v2.0.2](https://reprex.tidyverse.org)}