[Rd] readLines interaction with gsub different in R-dev

Hugh Parsonage
Sat, 17 Feb 2018 15:35:59 -0000

| Confirmed for R-devel (current) on Ubuntu 17.10.  But ... isn't the regexp
| you use wrong, ie isn't R-devel giving the correct answer?

No, I don't think R-devel is correct (or at least consistent with the
documentation). My interpretation of gsub("(\\w)", "\\U\\1",
entry,
perl = TRUE) is "Take every word character and replace it with itself,
converted to uppercase."

Perhaps my example was too minimal. Consider the following:

R> gsub("(\\w)", "\\U\\1", entry, perl = TRUE)
[1] "A"

R> gsub("(\\w)", "\\1", entry, perl = TRUE)
[1] "author: Am?lie"   # OK, but very different to 'A',
despite only
not specifying uppercase

R> gsub("(\\w)", "\\U\\1", "author: Amelie",
perl = TRUE)
[1] "AUTHOR: AMELIE"  # OK, but very different to 'A',

R> gsub("^(\\w+?): (\\w)", "\\U\\1\\E: \\2", entry, perl
= TRUE)
 "AUTHOR"  # Where did everything after the first group go?

I should note the following example too:
R> gsub("(\\w)", "\\U\\1", entry, perl = TRUE, useBytes =
TRUE)
[1] "AUTHOR: AM??LIE"  # latin1 encoding


A call to `readLines` (possibly `scan()` and `read.table` and friends)
is essential.




On 18 February 2018 at 02:15, Dirk Eddelbuettel <edd at debian.org>
wrote:
>
> On 17 February 2018 at 21:10, Hugh Parsonage wrote:
> | I was told to re-raise this issue with R-dev:
> |
> | In the documentation of R-dev and R-3.4.3, under ?gsub
> |
> | > replacement
> | >    ... For perl = TRUE only, it can also contain "\U" or
"\L" to convert the rest of the replacement to upper or lower case and
"\E" to end case conversion.
> |
> | However, the following code runs differently:
> |
> | tempf <- tempfile()
> | writeLines(enc2utf8("author: Am?lie"), con = tempf, useBytes =
TRUE)
> | entry <- readLines(tempf, encoding = "UTF-8")
> | gsub("(\\w)", "\\U\\1", entry, perl = TRUE)
> |
> |
> | "AUTHOR: AM?LIE"  # R-3.4.3
> |
> | "A"                              # R-dev
>
> Confirmed for R-devel (current) on Ubuntu 17.10.  But ... isn't the
regexp
> you use wrong, ie isn't R-devel giving the correct answer?
>
> R> tempf <- tempfile()
> R> writeLines(enc2utf8("author: Am?lie"), con = tempf,
useBytes = TRUE)
> R> entry <- readLines(tempf, encoding = "UTF-8")
> R> gsub("(\\w)", "\\U\\1", entry, perl = TRUE)
> [1] "A"
> R> gsub("(\\w+)", "\\U\\1", entry, perl = TRUE)
> [1] "AUTHOR"
> R> gsub("(.*)", "\\U\\1", entry, perl = TRUE)
> [1] "AUTHOR: AM?LIE"
> R>
>
> Dirk
>
> --
> http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org