different output using stringi and gsub (using the same pattern on the same string)

Question

I wish to know why I obtain two different output strings by using gsub and stringi. Does the metacharacter "." not include new lines in stringi? Does stringi read "line by line"?

By the way I did not find any way to perform the "correct" substitution with stringi so I needed to use gsub here.

string <- "is it normal?\n\nhttp://www.20minutes.fr"

> gsub(" .*?http"," http", string)
[1] "is http://www.20minutes.fr"

> stri_replace_all_regex(string, " .*?http"," http")
[1] "is it normal?\n\nhttp://www.20minutes.fr"

Try `stri_replace_all_regex(string, " .*?http"," http", opts_regex = stri_opts_regex(dotall = TRUE))`. — lukeA, Apr 15 '15 at 09:47
yep. By the way also this works: `stri_replace_all_regex(string, "(?s) .*?http"," http")` By the way I consider this behaviour weird! — Dario Lacan, Apr 15 '15 at 10:28

score 3 · Accepted Answer · answered Apr 15 '15 at 11:03

3

One way would be to set . to also match line terminators instead of stopping at a line:

stri_replace_all_regex(string, " .*?http"," http", 
                       opts_regex = stri_opts_regex(dotall = TRUE))

answered Apr 15 '15 at 11:03

lukeA

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Do you know why they changed the standard R (posix) regex behaviour? Is it in Perl that the dot does not match new lines? – Dario Lacan Apr 15 '15 at 18:08

score 2 · Answer 2 · answered May 01 '15 at 19:11

By default -- for historical reasons, see this tutorial -- in most regex engines a dot doesn't match a newline character. As @lukeA suggested, to match a newline you may set dotall option to TRUE in stringi regex-based functions.

By the way, gsub(..., perl=TRUE) gives results consistent with stringi.

different output using stringi and gsub (using the same pattern on the same string)

2 Answers2