[R] Regular Expressions Help

maud maud.july at gmail.com
Sat Apr 19 06:46:13 CEST 2008

I am having some trouble learning regular expressions. Let me describe
the general problem I am dealing with. Consider the following setup:

Joe<- c(1,2,3)
Bob<- c(2,4,6)
Alice <- c(9,8,7)

Matrix <- cbind(Joe, Bob, Alice)
St <- c("Bob", "Alice", "Alice:Bob")

Now I want to make a new matrix having only the column's listed in St
that were in Matrix (which I can do). However, In addition for
elements of the form "Alice:Bob" I want to make a new column in my new
matrix with the product of these columns. I am not sure if a semicolon
is a valid symbol for a column name, if not we can replace it with
something like qqq.

I have been reading over various post on regular expressions, but
really haven't made any progress. As far as I can tell there aren't
standard string functions in R. (Also, as an aside, is there a
wildcard character in R? I'd want something so if x="Bob" a statment
of the form x== "B*b" would evaluate true where * is the wildcard.)

 Any help would be appreciated!

(also, thanks again to those who helped on my last question!)

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