Dealing with commas in a CSV file

Question

I am looking for suggestions on how to handle a csv file that is being created, then uploaded by our customers, and that may have a comma in a value, like a company name.

Answer 1

As mentioned in my comment to harpo's answer, his solution is good and works in most cases, however in some scenarios when commas as directly adjacent to each other it fails to split on the commas.

This is because of the Regex string behaving unexpectedly as a vertabim string. In order to get this behave correct, all " characters in the regex string need to be escaped manually without using the vertabim escape.

Ie. The regex should be this using manual escapes:

",(?=(?:[^\"\"]*\"\"[^\"\"]*\"\")*(?![^\"\"]*\"\"))"

which translates into ",(?=(?:[^""]*""[^""]*"")*(?![^""]*""))"

When using a vertabim string @",(?=(?:[^""]*""[^""]*"")*(?![^""]*""))" it behaves as the following as you can see if you debug the regex:

",(?=(?:[^"]*"[^"]*")*(?![^"]*"))"

So in summary, I recommend harpo's solution, but watch out for this little gotcha!

I've included into the CsvReader a little optional failsafe to notify you if this error occurs (if you have a pre-known number of columns):

if (_expectedDataLength > 0 && values.Length != _expectedDataLength) 
throw new DataLengthException(string.Format("Expected {0} columns when splitting csv, got {1}", _expectedDataLength, values.Length));

This can be injected via the constructor:

public CsvReader(string fileName, int expectedDataLength = 0) : this(new FileStream(fileName, FileMode.Open, FileAccess.Read))
{
    _expectedDataLength = expectedDataLength;
}