[R] detect escape character

[David Winsemius]

On Jun 3, 2014, at 11:03 AM, Adrian Dușa wrote:

> Dear All,
> 
> I should be knowing this, but not get it right...

I'm a little surprised to see you ask this, too, but we each have lacunae in our R knowledge, so I hope this helps:

> s <- scan(what="")  # Assuming you were asking about items coming in from ASCII data files
1: Man\Woman
2: 
Read 1 item
> s
[1] "Man\\Woman"
> gsub("\\", "/", s)
Error in gsub("\\", "/", s) : 
  invalid regular expression '\', reason 'Trailing backslash'

> gsub("\\\\", "/", s)
[1] "Man/Woman"

_Each_ of the backslashes in what you might have thought would succeed ("\\") also needed their own backslash. The first doubled backslash becomes a real "escape"-character in the pattern and the second doubled backslash becomes an ordinary ASCII backslash character.

-- 
David.

> For a string like this:
> 
> "Man\Woman"
> 
> I would like to detect the escape character "\" and replace it with "/".
> 
> Tried various ways using gsub(), but don't get it right yet. Any suggestion
> would be highly welcomed...
> 
> Thank you,
> Adrian
> 
> -- 
> Adrian Dusa
> University of Bucharest
> Romanian Social Data Archive
> 1, Schitu Magureanu Bd.
> 050025 Bucharest sector 5
> Romania
> Tel.:+40 21 3126618 \
>        +40 21 3120210 / int.101
> Fax: +40 21 3158391
> 
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David Winsemius
Alameda, CA, USA