I would like to extract cat and dog in any order
string1 <- "aasdfadsf cat asdfadsf dog"
string2 <- "asfdadsfads dog asdfasdfadsf cat"
What I have now extracts cat and dog, but also the text in-between
stringr::str_extract(string1, "cat.*dog|dog.*cat"
I would like the output to be
cat dog
and
dog cat
for string1 and string2, respectively
You may use sub with the following PCRE regex:
.*(?|(dog).*(cat)|(cat).*(dog)).*
See the regex demo.
Details
.* - any 0+ chars other than line break chars (to match all chars add (?s) at the pattern start) (?|(dog).*(cat)|(cat).*(dog)) - a branch reset group (?|...|...) matching either of the two alternatives:
(dog).*(cat) - Group 1 capturing dog, then any 0+ chars as many as possible, and Group 2 capturing cat| - or(cat).*(dog) - Group 1 capturing cat, then any 0+ chars as many as possible, and Group 2 capturing dog (in a branch reset group, group IDs reset to the value before the group + 1).* - any 0+ chars other than line break charsThe \1 \2 replacement pattern inserts Group 1 and Group 2 values into the resulting string (so that the result is just dog or cat, a space, and a cat or dog).
See an R demo online, too:
x <- c("aasdfadsf cat asdfadsf dog", "asfdadsfads dog asdfasdfadsf cat")
sub(".*(?|(dog).*(cat)|(cat).*(dog)).*", "\\1 \\2", x, perl=TRUE)
## => [1] "cat dog" "dog cat"
To return NA in case of no match, use a regex to either match the specific pattern, or the whole string, and use it with gsubfn to apply custom replacement logic:
> gsubfn("^(?:.*((dog).*(giraffe)|(giraffe).*(dog)).*|.*)$", function(x,a,b,y,z,i) ifelse(nchar(x)>0, paste0(a,y," ",b,z), NA), x)
[1] "NA" "NA"
> gsubfn("^(?:.*((dog).*(cat)|(cat).*(dog)).*|.*)$", function(x,a,b,y,z,i) ifelse(nchar(x)>0, paste0(a,y," ",b,z), NA), x)
[1] "cat dog" "dog cat"
Here,
^ - start of the string anchor(?:.*((dog).*(cat)|(cat).*(dog)).*|.*) - a non-capturing group that matches either of the two alternatives:
.*((dog).*(cat)|(cat).*(dog)).*:
.* - any 0+ chars as many as possible((dog).*(cat)|(cat).*(dog)) - a capturing group matching either of the two alternatives:
(dog).*(cat) - dog (Group 2, assigned to a variable), any 0+ chars as many as possible, and then cat (Group 3, assigned to b variable)|(cat).*(dog) - dog (Group 4, assigned to y variable), any 0+ chars as many as possible, and then cat (Group 5, assigned to z variable).* - any 0+ chars as many as possible
| - or.* - any 0+ chars$ - end of the string anchor.The x in the anonymous function represents the Group 1 value that is "technical" here, we check if the Group 1 match length is not zero with nchar, and if it is not empty we replace with the custom logic, and if the Group 1 is empty, we replace with NA.
We can use str_extract_all from the stringr package with capture groups.
string1 <- "aasdfadsf cat asdfadsf dog"
string2 <- "asfdadsfads dog asdfasdfadsf cat"
string3 <- "asfdadsfads asfdadsfadf"
library(stringr)
str_extract_all(c(string1, string2, string3), pattern = "(dog)|(cat)")
# [[1]]
# [1] "cat" "dog"
#
# [[2]]
# [1] "dog" "cat"
#
# [[3]]
# character(0)
We can also set simplify = TRUE. The output would be a matrix.
str_extract_all(c(string1, string2, string3), pattern = "(dog)|(cat)", simplify = TRUE)
# [,1] [,2]
# [1,] "cat" "dog"
# [2,] "dog" "cat"
# [3,] "" ""
Or,
> regmatches(string1,gregexpr("cat|dog",string1))
[[1]]
[1] "cat" "dog"
> regmatches(string2,gregexpr("cat|dog",string2))
[[1]]
[1] "dog" "cat"
