怎么说（\\ w + \\ W +）乘以正则表达式4（R gsub）

Question

(In R gsub(),) I need to capture the four words occurring after a particular phrase in a bigger string. Building on the wisdom offered here , I came up with: ^.*\\\\b(particular phrase)\\\\W+(\\\\w+\\\\W+\\\\w+\\\\W+\\\\w+\\\\W+\\\\w+).*$

For example:

this_txt <- "Blah blah particular phrase Extract These Words Please for the blah blah. Ignore blah this other stuff blah blah, blah."
this_pattern <- "^.*\\b(particular phrase)\\W+(\\w+\\W+\\w+\\W+\\w+\\W+\\w+).*$"
gsub(this_pattern, "\\2", this_txt, ignore.case = T)
# [1] "Extract These Words Please"

But the repetition of \\\\w+\\\\W+ in the pattern is pretty unseemly. Surely there is a better way. I thought ^.*\\\\b(particular phrase)\\\\W+(\\\\w+\\\\W+){4}.*$ might work, but it doesn't.

Answer 1

You may use

^.*\b(particular phrase)\W+((?:\w+\W+){3}\w+).*$

In R,

this_pattern <- "^.*\\b(particular phrase)\\W+((?:\\w+\\W+){3}\\w+).*$"

See the regex demo

(\\w+\\W+\\w+\\W+\\w+\\W+\\w+) is replaced with ((?:\\w+\\W+){3}\\w+) . The ((?:\\w+\\W+){3}\\w+) is a capturing group ( (...) ) that contains two subpatterns:

• (?:\\w+\\W+){3} - a non-capturing group matching three repetitions of
  • \\w+ - 1 or more word chars
  • \\W+ - 1 or more non-word chars
• \\w+ - 1 or mor word chars.