是否有R函数提取所有数字，然后提取特定的模式？

Question

I am working R. I want to extract all numbers between the last blank space and a string pattern ("-APPLE") in a vector. The numbers can be of variable length.

test_string = c("ABC 2-APPLE", "123 25-APPLE", "DEF GHI 567-APPLE", "ORANGE")

Expected Result set should be a vector as in c(2, 25, 567, NA)

Answer 1

See Regex group capture in R with multiple capture-groups for an example of using str_match() , from the stringr package.

In your case:

> test_string = c("ABC 2-APPLE", "123 25-APPLE", "DEF GHI 567-APPLE")
> 
> library(stringr)
> x <- str_match(test_string, " ([0-9]+)-APPLE$")[,2]
> as.numeric(x)
[1]   2  25 567

Answer 2

you can use the "rebus" package, which is very user-friendly in creating the regex patterns you need.

library(rebus)
## adjust the lo and hi arguments of dgt() based on your text

rx <- lookbehind(SPACE) %R% dgt(1,5) %R% lookahead("-APPLE")
str_extract(test_string, rx)