Why isn't \\b in gsubfn in R working for me?

Question

I have a string like this:

vect <- c("Thin lines are not great, I am in !!! AND You shouldn't be late OR you loose")

I want to replace, "in" to %in%", "AND" to "&", "OR" to "|".

I know this can be done using gsub like below:

gsub("\\bin\\b","%in%", vect),

but I need three different lines for each of the replacement, hence I choose to use gsubfn .

so I tried,

gsubfn("\\bin\\b|\\bAND\\b|\\bOR\\b", list("in"="%in%", "AND"= "&", "OR"="|"), vect)

but It returns a string with nothing changed, for some reason \\\\b is not working for the string. However, \\\\b does work great with gsub and I am able to replace all the three strings in by piping together using gsub .

My question is, why \\\\b is not working inside gsubfn . what I am missing inside my regex?

Please help.

Output should be:

"Thin lines are not great, I am %in% !!! & You shouldn't be late | you loose"

This works:

gsubfn("\\w+", list("in"="%in%", "AND"= "&", "OR"="|"), vect)

Answer 1

By default, Tcl regex engine is used, see gsubfn docs :

If the R installation has tcltk capability then the tcl engine is used unless FUN is a proto object or perl=TRUE in which case the "R" engine is used (regardless of the setting of this argument).

So, word boundaries are defined with \\y :

> gsubfn("\\y(in|AND|OR)\\y", list("in"="%in%", "AND"= "&", "OR"="|"), vect)
[1] "Thin lines are not great, I am %in% !!! & You shouldn't be late | you loose"

Ainother way is by using \\m as leading word boundary and \\M for a trailing word boundary:

> gsubfn("\\m(in|AND|OR)\\M", list("in"="%in%", "AND"= "&", "OR"="|"), vect)
[1] "Thin lines are not great, I am %in% !!! & You shouldn't be late | you loose"

You may pass perl=TRUE and use \\b :

> gsubfn("\\b(in|AND|OR)\\b", list("in"="%in%", "AND"= "&", "OR"="|"), vect, perl=TRUE)
[1] "Thin lines are not great, I am %in% !!! & You shouldn't be late | you loose"

Answer 2

Add perl = T that should do it.

gsubfn("\\bin\\b|\\bAND\\b|\\bOR\\b", list("in"="%in%", "AND"= "&", "OR"="|"), vect, perl =T)

Output

[1] "Thin lines are not great, I am %in% !!! & You shouldn't be late | you loose"

---

From gsub documentation

The POSIX 1003.2 mode of gsub and gregexpr does not work correctly with repeated word-boundaries (eg, pattern = "\\b"). Use perl = TRUE for such matches (but that may not work as expected with non-ASCII inputs, as the meaning of 'word' is system-dependent).

And gsubfn documentation

... Other gsub arguments.

Doesn't explain why gsub works fine without the perl argument, but to do gsubfn it needs the perl=T