R help - Jan 2006 - How do I get sub to insert a single backslash?

Something about the way R processes backslashes is defeating me.
Perhaps this is because I have only just started using R for text processing.

I would like to change occurrences of the ampersand & into ampersand 
preceded by a backslash.

 > temp <- "R & D"
 > sub("&", "\&", temp)
[1] "R & D"
 > sub("&", "\\&", temp)
[1] "R & D"
 > sub("&", "\\\&", temp)
[1] "R & D"
 > sub("&", "\\\\&", temp)
[1] "R \\& D"
 >

So I can get zero, or two backslashes, but not one. I am sure this is 
really simple but I did not find the answer by doing, for example ?regexp 
or ?Quotes


Michael Dewey
http://www.aghmed.fsnet.co.uk

Michael Dewey <info at aghmed.fsnet.co.uk> writes:
> Something about the way R processes backslashes is defeating me.
> Perhaps this is because I have only just started using R for text
processing.
> 
> I would like to change occurrences of the ampersand & into ampersand 
> preceded by a backslash.
> 
>  > temp <- "R & D"
>  > sub("&", "\&", temp)
> [1] "R & D"
>  > sub("&", "\\&", temp)
> [1] "R & D"
>  > sub("&", "\\\&", temp)
> [1] "R & D"
>  > sub("&", "\\\\&", temp)
> [1] "R \\& D"
>  >
> 
> So I can get zero, or two backslashes, but not one. I am sure this is 
> really simple but I did not find the answer by doing, for example ?regexp 
> or ?Quotes

None of those result strings  have two backslashes!


Hint:
> nchar("R \\& D")
[1] 6

and ?Quotes tellse the entire story.

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