Question

What is the regular expression to split on comma (,) except if surrounded by double quotes? For example:

max,emily,john = ["max", "emily", "john"]

BUT

max,"emily,kate",john = ["max", "emily,kate", "john"]

Looking to use in C#: Regex.Split(string, "PATTERN-HERE");

Thanks.

Answer 1

Situations like this often call for something other than regular expressions. They are nifty, but patterns for handling this kind of thing are more complicated than they are useful.

You might try something like this instead:

public static IEnumerable<string> SplitCSV(string csvString)
{
    var sb = new StringBuilder();
    bool quoted = false;

    foreach (char c in csvString) {
        if (quoted) {
            if (c == '"')
                quoted = false;
            else
                sb.Append(c);
        } else {
            if (c == '"') {
                quoted = true;
            } else if (c == ',') {
                yield return sb.ToString();
                sb.Length = 0;
            } else {
                sb.Append(c);
            }
        }
    }

    if (quoted)
        throw new ArgumentException("csvString", "Unterminated quotation mark.");

    yield return sb.ToString();
}

It probably needs a few tweaks to follow the CSV spec exactly, but the basic logic is sound.