Ruby regex to match a space without a leading comma

Question

How can I match a space without a leading comma?

My use case is I would like to split a string on space without a leading comma e.g. "id 10, 11"

Yup so basically for a string `"id 10, 11"` I only care about "id 10". After splitting I would end up with `["id", "10"]` — Elvyn Mejia, Nov 15 '17 at 22:11
What if there are two spaces after `,`? Should it split on the second space? Also, see https://ideone.com/XTcSsP. Your question is too unclear. Please explain the expected output for the given example string, and why it should look like that. — Wiktor Stribiżew, Nov 15 '17 at 22:24
Without an idea of what you're looking to get as output, this is very confusingly worded. Also you haven't attempted to solve the problem, so I'm voting to close. — Mark Thomas, Nov 15 '17 at 23:34

score 2 · Answer 1 · answered Nov 15 '17 at 22:14

2

 'id 10, 11'.split(/(?<=[^,])[ ]/)

Output:

=> ["id", "10, 11"]

answered Nov 15 '17 at 22:14

eugene-nikolaev

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what if only want `=> ["id", "10"]` – Elvyn Mejia Nov 15 '17 at 22:18

score 1 · Answer 2 · answered Nov 15 '17 at 23:25

1

No need for a regex, just split twice:

"id 10, 11".split(",").first.split #=> ["id", "10"]

answered Nov 15 '17 at 23:25

steenslag

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Cary Swoveland · Answer 3 · 2017-11-16T01:24:43.680

You could use the regular expression

r = /(?<!,) /

which reads, "match one space not preceded by a space" ((?!,) being a negative lookbehind).

"fe, fi, fo and fum".split r
   #=> ["fe, fi, fo", "and", "fum"]
"fe, fi,     fo\nand fum".split r
   #=> ["fe, fi, ", "", "", "", "fo\nand", "fum"]

If one wishes to break on one or more spaces not preceded by a comma, use

r = /(?<!,) +/
"fe, fi,     fo\nand fum".split r
  #=> ["fe, fi, ", "fo\nand", "fum"]

To split on one or more whitespace characters not preceded by a comma, use

r = /(?<!,)\s+/
"fe, fi,     fo\nand fum".split r
  #=> ["fe, fi, ", "fo", "and", "fum"]

It may prudent to first perform String#lstrip.

r = /(?<!,)\s+/
" fe, fi,     fo\nand fum ".split r
  #=> ["", "fe, fi, ", "fo", "and", "fum"]
" fe, fi,     fo\nand fum ".lstrip.split r
  #=> ["fe, fi, ", "fo", "and", "fum"]

Depending on requirements, one could instead take @elyvn's advice and write

r = /(?<=[^,])\s+/

which reads, "match one or more whitespace characters preceded by a character other than a comma" ((?<=[^,]) being positive lookbehind).

" fe, fi,     fo\nand fum ".split r
  #=> [" fe, fi, ", "fo", "and", "fum"]

Ruby regex to match a space without a leading comma

3 Answers3