Gsub正则表达式替换

Question

I am trying to do a gsub replacement in R. I would like to identify two terms from two lists separated by a single whitespace and replace it with an underscore. I have successfully identified the match but I am not experienced enough in regex to understand the gsub documentation. Can somebody help write the gsub ?

Right now I have:

gsub("(a|b|c)\\s+(x|y|z)","(a|b|c)_(x|y|z)",a x)

(Note: there are several places in the string that match this if that matters)

I want to go from:
ax -> a_x
bz -> b_z
hello world bx how are az you -> hello world b_x how are a_z you... and so on.

Instead it does:
ax -> (a|b|c) (x|y|z)
bz -> (a|b|c) (x|y|z) ... and so on.

If anyone wants to drop a little theory in that would be appreciated but I'm working on a deadline so a simultaneous answer would be ideal.

Thanks.

Answer 1

You have to use \\\\1 and \\\\2 to replace the term inside the first and second () with itself.

vec <- "hello world b x how are a z you"

gsub("(a|b|c)\\s+(x|y|z)","\\1_\\2", vec)
# [1] "hello world b_x how are a_z you"