[R] How do I get sub to insert a single backslash?

[Michael Dewey]

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