ianmcook commented on a change in pull request #9143:
URL: https://github.com/apache/arrow/pull/9143#discussion_r554277501
##########
File path: r/R/dataset-format.R
##########
@@ -104,9 +104,31 @@ CsvFileFormat$create <- function(..., opts =
csv_file_format_parse_options(...))
}
csv_file_format_parse_options <- function(...) {
+ opt_names <- names(list(...))
# Support both the readr spelling of options and the arrow spelling
- readr_opts <- c("delim", "quote", "escape_double", "escape_backslash",
"skip_empty_rows")
- if (any(readr_opts %in% names(list(...)))) {
+ arrow_opts <- names(formals(CsvParseOptions$create))
+ readr_opts <- names(formals(readr_to_csv_parse_options))
+ is_arrow_opt <- !is.na(pmatch(opt_names, arrow_opts))
+ is_readr_opt <- !is.na(pmatch(opt_names, readr_opts))
+ bad_opts <- opt_names[!is_arrow_opt & !is_readr_opt]
+ if (length(bad_opts)) {
+ stop("Unsupported options: ",
+ paste(bad_opts, collapse = ", "),
+ call. = FALSE)
+ }
+ is_ambig_opt <- is.na(pmatch(opt_names, c(arrow_opts, readr_opts)))
Review comment:
`arrow_opts` is a vector of the names of the allowed arguments to
`CsvParseOptions$create()` (Arrow-style arguments). `readr_opts` is a vector of
the names of the allowed arguments to `readr_to_csv_parse_options()`
(readr-style arguments).
```r
arrow_opts
## [1] "delimiter" "quoting" "quote_char"
"double_quote" "escaping"
## [6] "escape_char" "newlines_in_values" "ignore_empty_lines"
readr_opts
## [1] "delim" "quote" "escape_double"
"escape_backslash" "skip_empty_rows"
```
The function we're inside here (`csv_file_format_parse_options()`) allows
_either_ of these sets of arguments. These two sets of argument names are
mutually exclusive, but R's partial matching of argument names throws a wrench
in that. For example, if someone shortens either `delimiter` or `delim` to just
`del`, that would work fine in a function that accepts _only_ Arrow-style
arguments or _only_ readr-style options, but here it creates ambiguity—we can't
tell if the user is intending to specify Arrow-style arguments or readr-style
arguments.
```r
open_dataset("/path/to/csv/", format = "csv", del = ";")
## đź’€
```
So `pmatch()` to the rescue. `pmatch()`, when called like it is here, uses
the same algorithm for partial matching that R uses to identify named arguments
in function calls. `pmatch(x, y)` returns a vector of the same length as `x`,
and in each position, the value will be `NA` if and only if the character
string in that position in `x` _cannot_ be unambiguously matched to exactly one
character string in `y`. So if there are any `NA` values in the vector returned
by `pmatch()`, that means at least one of the argument names is ambiguous.
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