[R] Regular expression help

[Duncan Murdoch]

I have a file containing "words" like


a

a/b

a/b/c

where there may be multiple words on a line (separated by spaces).  The 
a, b, and c strings can contain non-space, non-slash characters. I'd 
like to use gsub() to extract the c strings (which should be empty if 
there are none).

A real example is

"f 147/1315/587 2820/1320/587 3624/1321/587 1852/1322/587"

which I'd like to transform to

" 587 587 587 587"

Another real example is

"f 1067 28680 24462"

which should transform to "   ".

I've tried a few different regexprs, but am unable to find a way to say 
"transform words by deleting everything up to and including the 2nd 
slash" when there might be zero, one or two slashes.  Any suggestions?

Duncan Murdoch