CODEWITHSUNDEEP
regexrstringsubstringstring-matching
fstab
fstab

Reputation: 5029

R: extract list of matching parts of a string via regex

Let's say that I need to extract different parts from a string as list, for example I would like to divide the string "aaa12xxx" in three parts.

One possibility is to do three gsub calls:

parts = c()
parts[1] = gsub('([[:alpha:]]+)([0-9]+)([[:alpha:]]+)', '\\1', "aaa12xxx")
parts[2] = gsub('([[:alpha:]]+)([0-9]+)([[:alpha:]]+)', '\\2', "aaa12xxx")
parts[3] = gsub('([[:alpha:]]+)([0-9]+)([[:alpha:]]+)', '\\3', "aaa12xxx")

Of course this seems quite a waste (even if it's inside a for loop). Isn't there a function that simply returns the list of parts from a regex and a test string?

Upvotes: 3

Views: 924

Answers (2)

Avinash Raj
Avinash Raj

Reputation: 174696

Just split the input string through strsplit and get the parts you want..

> x <- "aaa12xxx"
> strsplit(x,"(?<=[[:alpha:]])(?=\\d)|(?<=\\d)(?=[[:alpha:]])", perl=TRUE)
[[1]]
[1] "aaa" "12"  "xxx"

Get the parts by specifying the index number..

> m <- unlist(strsplit(x,"(?<=[[:alpha:]])(?=\\d)|(?<=\\d)(?=[[:alpha:]])", perl=TRUE))
> m[1]
[1] "aaa"
> m[2]
[1] "12"
> m[3]
[1] "xxx"

  • (?<=[[:alpha:]])(?=\\d) Matches all the boundaries which are preceded by an alphabet and followed by a digit.

  • | OR

  • (?<=\\d)(?=[[:alpha:]]) Matches all the boundaries which are preceded by a digit and followed by an alphabet.

  • Splitting your input according to the matched boundaries will give you the desired output.

Upvotes: 4

vks
vks

Reputation: 67968

(\\d+)|([a-zA-Z]+)

or

([[:alpha:]]+)|([0-9]+)

You can just grab the capture.use str_match_all() from library(stringr).See demo.

https://regex101.com/r/fA6wE2/8

Upvotes: 3

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