Regex for Comma delimited list

What is the regular expression to validate a comma delimited list like this one:

12365, 45236, 458, 1, 99996332, ......

I suggest you to do in the following way:

(\d+)(,\s*\d+)*

which would work for a list containing 1 or more elements.

This regex extracts an element from a comma separated list, regardless of contents:

(.+?)(?:,|$)

If you just replace the comma with something else, it should work for any delimiter.

It depends a bit on your exact requirements. I'm assuming: all numbers, any length, numbers cannot have leading zeros nor contain commas or decimal points. individual numbers always separated by a comma then a space, and the last number does NOT have a comma and space after it. Any of these being wrong would simplify the solution.

([1-9][0-9],[ ])[1-9][0-9]*

Here's how I built that mentally:

[0-9]  any digit.
[1-9][0-9]*  leading non-zero digit followed by any number of digits
[1-9][0-9]*, as above, followed by a comma
[1-9][0-9]*[ ]  as above, followed by a space
([1-9][0-9]*[ ])*  as above, repeated 0 or more times
([1-9][0-9]*[ ])*[1-9][0-9]*  as above, with a final number that doesn't have a comma.

Match duplicate comma-delimited items:

(?<=,|^)([^,]*)(,\1)+(?=,|$)

Reference.

This regex can be used to split the values of a comma delimitted list. List elements may be quoted, unquoted or empty. Commas inside a pair of quotation marks are not matched.

,(?!(?<=(?:^|,)\s*"(?:[^"]|""|\\")*,)(?:[^"]|""|\\")*"\s*(?:,|$))

Reference.

/^\d+(?:, ?\d+)*$/

i used this for a list of items that had to be alphanumeric without underscores at the front of each item.

^(([0-9a-zA-Z][0-9a-zA-Z_]*)([,][0-9a-zA-Z][0-9a-zA-Z_]*)*)$

You might want to specify language just to be safe, but

(\d+, ?)+(\d+)?

ought to work

I had a slightly different requirement, to parse an encoded dictionary/hashtable with escaped commas, like this:

"1=This is something, 2=This is something,,with an escaped comma, 3=This is something else"

I think this is an elegant solution, with a trick that avoids a lot of regex complexity:

if (string.IsNullOrEmpty(encodedValues))
{
    return null;
}
else
{
    var retVal = new Dictionary<int, string>();
    var reFields = new Regex(@"([0-9]+)\=(([A-Za-z0-9\s]|(,,))+),");
    foreach (Match match in reFields.Matches(encodedValues + ","))
    {
        var id = match.Groups[1].Value;
        var value = match.Groups[2].Value;
        retVal[int.Parse(id)] = value.Replace(",,", ",");
    }
    return retVal;
}

I think it can be adapted to the original question with an expression like @"([0-9]+),\s?" and parse on Groups[0].

I hope it's helpful to somebody and thanks for the tips on getting it close to there, especially Asaph!

In JavaScript, use split to help out, and catch any negative digits as well:

'-1,2,-3'.match(/(-?\d+)(,\s*-?\d+)*/)[0].split(',');
// ["-1", "2", "-3"]
// may need trimming if digits are space-separated

The following will match any comma delimited word/digit/space combination

(((.)*,)*)(.)*