Validate comma separated list of numbers with regex

Question

This cases should match:

1.23
1
1,
1.2,4
1.23, 4
1.23, 4,
1, 2.34
1.

This cases should not:

1,,
1.234

So there can be trailing comma or dot, zero or one space after comma. Numbers can be integers or floats with up to two fractions.

I've made this regex, but it fails on numbers with more than two fractions: https://regex101.com/r/CLTP2j/75

/^(?:\d+(?:\.[\d{1,2}]*)?|\.[\d{1,2}]+)(?:,[\s]?(?:\d+(?:\.[\d{1,2}]*)?|\.[\d{1,2}]+))*$/

I'm validating input field in html while user is typing, so he can start typing number 1.12. — catchall, Feb 07 '20 at 10:55
Try `^\d*(?:\.\d{0,2})?(?:,(?!,)\s?\d*(?:\.\d{0,2})?)*$`, see [this demo](https://regex101.com/r/vSgVDS/1). — Wiktor Stribiżew, Feb 07 '20 at 10:57

Tim Biegeleisen · Accepted Answer · 2020-02-07T10:59:43.827

-1

Use the following regex:

^\d+(?:\.\d{0,2})?(?:,\s*\d+(?:\.\d{0,2})?)*,?$

Demo

Rather than giving the typical verbose (and illegible) full breakdown of the pattern I used, I will instead explain a simpler requirement. Let's say you wanted to validate a CSV list of capital letters, e.g.

A,B,C

The pattern you would use is:

^[A-Z](?:,[A-Z])*,?$

Note that the term on the right says to allow zero or more additions of comma followed by another letter. Your requirement also allows a trailing comma, so the above pattern includes that too.

edited Feb 07 '20 at 10:59

answered Feb 07 '20 at 10:49

Tim Biegeleisen

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Do you want to say it is a duplicate of [Comma Separated Numbers Regex](https://stackoverflow.com/questions/16620980/comma-separated-numbers-regex)? – Wiktor Stribiżew Feb 07 '20 at 11:01
No, it is not an exact duplicate. – Tim Biegeleisen Feb 07 '20 at 11:01
I agree. Your explanation hints at that though. Then your regex does not work because it does not allow the values OP regex does. – Wiktor Stribiżew Feb 07 '20 at 11:02
My regex is just an failed attempt. Tim's regex covers 99% of use cases. It allows single comma, though. But one can interpret it as trailing comma. – catchall Feb 07 '20 at 11:06
@catchall But your sample allowed input does include `1,`. If you don't want that, then just remove the `,?` from the end of the pattern. – Tim Biegeleisen Feb 07 '20 at 11:07
Yes, I meant this - ```,```. – catchall Feb 07 '20 at 11:07
So, this *is* a duplicate then. – Wiktor Stribiżew Feb 07 '20 at 11:13
@WiktorStribiżew If marking questions duplicate were a sport, you would be on Poland's roster in Tokyo 2020 `:-)` – Tim Biegeleisen Feb 07 '20 at 11:22
They are similar but not duplicate as Tim said. No I want the opposite - no bare comma allowed. Sorry for confusing you. – catchall Feb 07 '20 at 11:27
@catchall They are if Tim's answer is what you need. – Wiktor Stribiżew Feb 07 '20 at 11:34
Well maybe for someone who knows regex expressions very well. For me they are just similar. – catchall Feb 07 '20 at 11:40

Cary Swoveland · Answer 2 · 2020-02-09T19:14:14.927

If your objective is to determine if a string has the correct form, and not necessarily to use a regex applied to the entire string to make that determination, you could perform two steps, employing the following regular expressions:

r1 = /(?<!,), ?/
r2 = /^\d+(?:\.\d{,2})?$/

The steps are:

use r1 to split the string into one or more substrings
determine if all substrings match r2

r1 reads, "match a comma followed by at most one space and not preceded by a comma.

r2 reads, "match one or more digits at the beginning of the string, optionally followed by a decimal point then 0, 1 or 2 digits, followed by the end of the string".

In Ruby, for example, the following obtains:

arr =<<~END.split("\n")
1.23
1
1,
1.2,4
1.23, 4
1.23, 4,
1, 2.34
1,  2.34
1,,
1.234
END
  #=> ["1.23", "1", "1,", "1.2,4", "1.23, 4", "1.23, 4,", "1, 2.34",
  #    "1,  2.34", "1,,", "1.234"]

arr.each do |s|
  a = s.split r1
  result = a.all? { |t| t.match? r2 } ? "(Match)" : "(No match)"
  puts "%-9s: %-14s %s" % [s, a.inspect, result]
end

string     array          match?
---------------------------------
1.23     : ["1.23"]       (Match)
1        : ["1"]          (Match)
1,       : ["1"]          (Match)
1.2,4    : ["1.2", "4"]   (Match)
1.23, 4  : ["1.23", "4"]  (Match)
1.23, 4, : ["1.23", "4"]  (Match)
1, 2.34  : ["1", "2.34"]  (Match)
1,  2.34 : ["1", " 2.34"] (No match)
1,,      : ["1", ","]     (No match)
1.234    : ["1.234"]      (No match)

An important advantage of this approach is that testing is much easier than testing a single regular expression against the entire string, as r1 and r2 can be tested separately. This approach may also be more easily adaptable to changing requirements in future.

Validate comma separated list of numbers with regex

2 Answers2

Demo