问题
I need to find the number after the string "Count of". There could be a space or a symbol between the "Count of" string and the number. I have something that works on www.regex101.com but does not work with stringr str_extract function.
library(stringr)
shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2", "monkey coconut 3oz count of 5", "monkey coconut count of 50", "chicken Count Of-10")
str_extract(shopping_list, "count of ([\\d]+)")
[1] NA NA NA NA "count of 5" "count of 50" NA
What I want to get:
[1] NA NA NA NA "5" "50" "10"
回答1:
str_extract(shopping_list, "(?i)(?<=count of\\D)\\d+")
# [1] NA NA NA NA "5" "50" "10"
where (?i) makes the pattern case insensitive, \\D means not a number, and ?<= is a positive lookbehind.
回答2:
Look ahead and look behinds are what you are looking for with this grep...
shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2", "monkey coconut 3oz count of 5", "monkey coconut count of 50", "chicken Count Of-10")
str_extract(shopping_list, "(?<=count of )[0-9]*")
[1] NA NA NA NA "5" "50" NA
回答3:
as.numeric(sub("(?i).*count of.*?(\\d+).*", "\\1", shopping_list))
[1] NA NA NA NA 5 50 10
The regex pattern is:
(?i): Ignore case.*count of.*?: Any length of characters up to "count of"(\\d+): Capture one or more digits"\\1": Return the capture group
As of now the other answers will fail with something like ""coconut count of - 5" since they are constrained by one space after "count of".
来源：https://stackoverflow.com/questions/35947123/extract-number-after-specific-string