Regex for selecting substrings before and after a string

Question

I am trying to find a right regex expression to select substrings between another substring, which I'd like to exclude. For example in this string:

11 - 12£ in $ + 13

I want to select 12£ and $. Basically, it's substrings around in, until I hit an array of values I want to use as end/start, in this case, arithmetic operators %w(+ - / *)

So far closest I got was using this regex /(.\d\p{Sc})\sin\s(\p{Sc})/

Some more examples:

10 - 12$ in £ - 13$ should return 12$ and £

12 $ in £ should return 12$ and £

100£in$ should return 100£ and $

You will have to post process these matches anyway since you can't skip a part of a match. Easiest is to use (\d[\d\s]*\p{Sc})\sin\s(\p{Sc}) and remove whitespace from Group 1. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 15, 2017 at 14:57

ndnenkov · Accepted Answer · 2017-05-15 14:54:53Z

2

sentence.match(/[^-+*\/]*in[^-+*\/]*/).to_s.strip.split(/ *in */)

[^-+*\/]* matches multiple non-arithmetic operators
this will hence get everything from the "opening" to the "closing" operator that surround an in
#strip removes the leading and trailing whitespaces
finally, split into two strings, removing in and the spaces around it

answered May 15, 2017 at 14:54

ndnenkov

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3 Comments

Maxim Fedotov Over a year ago

This seem to work, but only going for one match. If I have 12£ in $ - 4$ in £ it'll only return first pair

ndnenkov Over a year ago

@MaximFedotov use scan and map instead.

seph Over a year ago

@MaximFedotov - You can do that with a scan: sentence.scan(/[^-+*\/]*in[^-+*\/]*/).map { |el| el.to_s.strip.split(/ *in */) }

Cary Swoveland · Accepted Answer · 2017-05-20 18:29:44Z

0

r = /
    \s+[+*\/-]\s+ # match 1+ whitespaces, 1 char in char class, 1+ whitespaces
    (\S+)         # match 1+ non-whitespaces in capture group 1
    \s+in\s+      # match 1+ whitespaces, 'in', 1+ whitespaces
    (\S+)         # match 1+ non-whitespaces in capture group 2
    \s+[+*\/-]\s  # match 1+ whitespaces, 1 char in char class, 1+ whitespaces
    /x            # free-spacing regex definition mode

str = '11 -     12£ in $ + 13 / 13F in   % * 4'
str.scan(r)
  #=> [["12£", "$"], ["13F", "%"]]

See the doc for String#scan to see how scan handles capture groups.

Note that '-' must be first or last in the character class [+*\/-].

edited May 20, 2017 at 18:29

answered May 15, 2017 at 16:21

Cary Swoveland

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