[R] string pattern matching

[Joe Ceradini]

Hi Folks,

Is there a way to find "x1 + x2 + x3" given "x1 + x3" as the pattern?
Or is that a ridiculous question, since I'm trying to find something
based on a pattern that doesn't exist?

test <- c("x1", "x2", "x3", "x1 + x2 + x3")
test
[1] "x1"           "x2"           "x3"           "x1 + x2 + x3"

grep("x1 + x2", test, fixed=TRUE, value = TRUE)
[1] "x1 + x2 + x3"


But what if only have "x1 + x3" as the pattern and still want to
return "x1 + x2 + x3"?

grep("x1 + x3", test, fixed=TRUE, value = TRUE)
character(0)

I'm sure this looks like an odd question. I'm trying to build a
function and stuck on this. Rather than dropping the whole function on
the list, I thought I'd try one piece I needed help with...although I
suspect that this question itself probably does bode well for my
function :)

Thanks!
Joe