grep and regrex for R phone numbers - r

Question

I would like to get the phone numbers from a file. I know the numbers have different forms, I don't know how to code for each form. Using grep and regrexpr in R. The numbers are written in this form:
xxx-xxx-xxxx ,
(xxx)xxx-xxxx,
xxx xxx xxxx,
xxx.xxx.xxxx

Answer 1

Try this:
phones <- c("foo 111-111-1111 bar" , "[phone] quux", "who knows 111 111 1111", "111.111.1111 I do", "111)111-1111 should not work", "1111111111 ditto", "a 111-111-1111 b [phone] c")
re <- gregexpr("(\\(\\d{3}\\)|\\d{3}[-. ])\\d{3}[-. ]\\d{4}", phones)
regmatches(phones, re)
# [[1]]
# [1] "111-111-1111"
# [[2]]
# [1] "[phone]"
# [[3]]
# [1] "111 111 1111"
# [[4]]
# [1] "111.111.1111"
# [[5]]
# character(0)
# [[6]]
# character(0)
# [[7]]
# [1] "111-111-1111" "[phone]"
In the data, I provide a few examples with other text on both, either, and neither side, as well as two examples that should not match. (That is: a starter "test set", as you want to make sure you both match good examples and no-match bad examples.) The last one hopes to match multiple numbers in one string/sentence.
gregexpr and regmatches are useful for finding and extracting or replacing regex-substrings within 1+ strings. For a "replace" example, one could do:
regmatches(phones, re) <- "GONE!"
phones
# [1] "foo GONE! bar" "GONE! quux"
# [3] "who knows GONE!" "GONE! I do"
# [5] "111)111-1111 should not work" "1111111111 ditto"
# [7] "a GONE! b GONE! c"
Obviously contrived replacement but certainly usable. Note though that regmatches operates in side-effect, meaning that it modified the phones vector in-place instead of returning the value. It's possible to force it to operate not in side-effect, but it is a little less intuitive:
phones # I reset it to the original value
# [1] "foo 111-111-1111 bar" "[phone] quux"
# [3] "who knows 111 111 1111" "111.111.1111 I do"
# [5] "111)111-1111 should not work" "1111111111 ditto"
# [7] "a 111-111-1111 b [phone] c"
`regmatches<-`(phones, re, value = "GONE!")
# [1] "foo GONE! bar" "GONE! quux"
# [3] "who knows GONE!" "GONE! I do"
# [5] "111)111-1111 should not work" "1111111111 ditto"
# [7] "a GONE! b GONE! c"
phones
# [1] "foo 111-111-1111 bar" "[phone] quux"
# [3] "who knows 111 111 1111" "111.111.1111 I do"
# [5] "111)111-1111 should not work" "1111111111 ditto"
# [7] "a 111-111-1111 b [phone] c"
Edit: scope-creep.
out <- unlist(Filter(length, regmatches(phones, re)))
out
# [1] "111-111-1111" "[phone]" "111 111 1111" "111.111.1111" "111-111-1111"
# [6] "[phone]"
gsub("[^0-9]", "", out)
# [1] "1111111111" "1111111111" "1111111111" "1111111111" "1111111111" "2222222222"
out <- gsub("[^0-9]", "", out)
sprintf("(%s)%s-%s", substr(out, 1, 3), substr(out, 4, 6), substr(out, 7, 10))
# [1] "[phone]" "[phone]" "[phone]" "[phone]" "[phone]"
# [6] "[phone]"