R: Extract N characters after M regex matches in one string

Question

I'm having difficulties in extracting exactly N characters after all regex matches in one string. E.g. N=3, and regex match is an opening bracket "(", and may be paste an aux word in between if M >= 1.

x1 = "use actual (Mon 3)|(Tue 4)"
x2 = "use actual (Mon 10)"
x3 = "use actual"

Desired outputs are:

"Mon and Tue"
"Mon"
""

I started with gsub( ".*\\(", "", c("use actual (Mon 3)|(Tue 4)")) and then tried to follow R extract part of string but got lost in ? and wildcards. Thanks!

Suppose if there are three brackets, would that be `Mon and Tue and Wed` — akrun, Apr 29 '15 at 20:37

score 4 · Accepted Answer · edited Jun 20 '20 at 09:12

4

try

 library(stringr)
 sapply(str_extract_all(x, perl('(?<=\\()[A-Za-z]{3}')),
             paste, collapse=' and ')
 #[1] "Mon and Tue"         "Mon"                 ""                   
 #[4] "Mon and Tue and Wed" "Mon"

data

 x4 <- "use actual (Mon 3)|(Tue 4)|(Wed 5)"
 x5 <- "foo (Mond bar)"
 x <- c(x1, x2, x3, x4, x5)

edited Jun 20 '20 at 09:12

Community

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answered Apr 29 '15 at 20:39

akrun

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Thank you! It works great! I'm not 100% following where N=3 characters is specified (in case I need arbitrary N after a match?) – Alexey Ferapontov Apr 29 '15 at 20:44
@AlexeyFerapontov I am extracting the character elements `[A-Za-z]+` that comes after a `(` which is used in the lookaround to match. So, it will extract all the cases that follow the pattern. – akrun Apr 29 '15 at 20:47
Is there a way to extract exactly 3 char? E.g. if string is `foo (Mond bar)` and I will still need only `Mon`? – Alexey Ferapontov Apr 29 '15 at 20:49
1

@AlexeyFerapontov I updated the post, Sorry I didn't read your earlier comment properly. – akrun Apr 29 '15 at 20:51
Ah, indeed `{3}` is the solution. Thank you again! – Alexey Ferapontov Apr 29 '15 at 20:53

R: Extract N characters after M regex matches in one string

1 Answers1

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