In C#, using the Regex
class, how does one parse comma-separated values, where some values might be quoted strings themselves containing commas?
using System ;
using System.Text.RegularExpressions ;
class Example
{
public static void Main ( )
{
string myString = "cat,dog,\"0 = OFF, 1 = ON\",lion,tiger,'R = red, G = green, B = blue',bear" ;
Console.WriteLine ( "\nmyString is ...\n\t" + myString + "\n" ) ;
Regex regex = new Regex ( "(?<=,(\"|\')).*?(?=(\"|\'),)|(^.*?(?=,))|((?<=,).*?(?=,))|((?<=,).*?$)" ) ;
Match match = regex.Match ( myString ) ;
int j = 0 ;
while ( match.Success )
{
Console.WriteLine ( j++ + " \t" + match ) ;
match = match.NextMatch() ;
}
}
}
Output (in part) appears as follows:
0 cat
1 dog
2 "0 = OFF
3 1 = ON"
4 lion
5 tiger
6 'R = red
7 G = green
8 B = blue'
9 bear
However, desired output is:
0 cat
1 dog
2 0 = OFF, 1 = ON
3 lion
4 tiger
5 R = red, G = green, B = blue
6 bear
Ah, RegEx. Now you have two problems. ;)
I'd use a tokenizer/parser, since it is quite straightforward, and more importantly, much easier to read for later maintenance.
This works, for example:
using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text;
class Program
{
static void Main(string[] args)
{
string myString = "cat,dog,\"0 = OFF, 1 = ON\",lion,tiger,'R = red, G = green, B = blue',bear";
Console.WriteLine("\nmyString is ...\n\t" + myString + "\n");
CsvParser parser = new CsvParser(myString);
Int32 lineNumber = 0;
foreach (string s in parser)
{
Console.WriteLine(lineNumber + ": " + s);
}
Console.ReadKey();
}
}
internal enum TokenType
{
Comma,
Quote,
Value
}
internal class Token
{
public Token(TokenType type, string value)
{
Value = value;
Type = type;
}
public String Value { get; private set; }
public TokenType Type { get; private set; }
}
internal class StreamTokenizer : IEnumerable<Token>
{
private TextReader _reader;
public StreamTokenizer(TextReader reader)
{
_reader = reader;
}
public IEnumerator<Token> GetEnumerator()
{
String line;
StringBuilder value = new StringBuilder();
while ((line = _reader.ReadLine()) != null)
{
foreach (Char c in line)
{
switch (c)
{
case '\'':
case '"':
if (value.Length > 0)
{
yield return new Token(TokenType.Value, value.ToString());
value.Length = 0;
}
yield return new Token(TokenType.Quote, c.ToString());
break;
case ',':
if (value.Length > 0)
{
yield return new Token(TokenType.Value, value.ToString());
value.Length = 0;
}
yield return new Token(TokenType.Comma, c.ToString());
break;
default:
value.Append(c);
break;
}
}
// Thanks, dpan
if (value.Length > 0)
{
yield return new Token(TokenType.Value, value.ToString());
}
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
internal class CsvParser : IEnumerable<String>
{
private StreamTokenizer _tokenizer;
public CsvParser(Stream data)
{
_tokenizer = new StreamTokenizer(new StreamReader(data));
}
public CsvParser(String data)
{
_tokenizer = new StreamTokenizer(new StringReader(data));
}
public IEnumerator<string> GetEnumerator()
{
Boolean inQuote = false;
StringBuilder result = new StringBuilder();
foreach (Token token in _tokenizer)
{
switch (token.Type)
{
case TokenType.Comma:
if (inQuote)
{
result.Append(token.Value);
}
else
{
yield return result.ToString();
result.Length = 0;
}
break;
case TokenType.Quote:
// Toggle quote state
inQuote = !inQuote;
break;
case TokenType.Value:
result.Append(token.Value);
break;
default:
throw new InvalidOperationException("Unknown token type: " + token.Type);
}
}
if (result.Length > 0)
{
yield return result.ToString();
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
Try with this Regex:
"[^"\r\n]*"|'[^'\r\n]*'|[^,\r\n]*
Regex regexObj = new Regex(@"""[^""\r\n]*""|'[^'\r\n]*'|[^,\r\n]*");
Match matchResults = regexObj.Match(input);
while (matchResults.Success)
{
Console.WriteLine(matchResults.Value);
matchResults = matchResults.NextMatch();
}
Ouputs:
Note: This regex solution will work for your case, however I recommend you to use a specialized library like FileHelpers.
Why not heed the advice from the experts and Don't roll your own CSV parser.
Your first thought is, "I need to handle commas inside of quotes."
Your next thought will be, "Oh, crap, I need to handle quotes inside of quotes. Escaped quotes. Double quotes. Single quotes..."
It's a road to madness. Don't write your own. Find a library with an extensive unit test coverage that hits all the hard parts and has gone through hell for you. For .NET, use the free and open source FileHelpers library.
it's not a regex, but I've used Microsoft.VisualBasic.FileIO.TextFieldParser to accomplish this for csv files. yes, it might feel a little strange adding a reference to Microsoft.VisualBasic in a C# app, maybe even a little dirty, but hey it works.
Just adding the solution I worked on this morning.
var regex = new Regex("(?<=^|,)(\"(?:[^\"]|\"\")*\"|[^,]*)");
foreach (Match m in regex.Matches("<-- input line -->"))
{
var s = m.Value;
}
As you can see, you need to call regex.Matches() per line. It will then return a MatchCollection with the same number of items you have as columns. The Value property of each match is, obviously, the parsed value.
This is still a work in progress, but it happily parses CSV strings like:
2,3.03,"Hello, my name is ""Joshua""",A,B,C,,,D
CSV is not regular. Unless your regex language has sufficient power to handle the stateful nature of csv parsing (unlikely, the MS one does not) then any pure regex solution is a list of bugs waiting to happen as you hit a new input source that isn't quite handled by the last regex.
CSV reading is not that complex to write as a state machine since the grammar is simple but even so you must consider: quoted quotes, commas within quotes, new lines within quotes, empty fields.
As such you should probably just use someone else's CSV parser. I recommend CSVReader for .Net
Function:
private List<string> ParseDelimitedString (string arguments, char delim = ',')
{
bool inQuotes = false;
bool inNonQuotes = false; //used to trim leading WhiteSpace
List<string> strings = new List<string>();
StringBuilder sb = new StringBuilder();
foreach (char c in arguments)
{
if (c == '\'' || c == '"')
{
if (!inQuotes)
inQuotes = true;
else
inQuotes = false;
}else if (c == delim)
{
if (!inQuotes)
{
strings.Add(sb.Replace("'", string.Empty).Replace("\"", string.Empty).ToString());
sb.Remove(0, sb.Length);
inNonQuotes = false;
}
else
{
sb.Append(c);
}
}
else if ( !char.IsWhiteSpace(c) && !inQuotes && !inNonQuotes)
{
if (!inNonQuotes) inNonQuotes = true;
sb.Append(c);
}
}
strings.Add(sb.Replace("'", string.Empty).Replace("\"", string.Empty).ToString());
return strings;
}
Usage
string myString = "cat,dog,\"0 = OFF, 1 = ON\",lion,tiger,'R = red, G = green, B = blue',bear, text";
List<string> strings = ParseDelimitedString(myString);
foreach( string s in strings )
Console.WriteLine( s );
Output:
cat
dog
0 = OFF, 1 = ON
lion
tiger
R = red, G = green, B = blue
bear
text
I found a few bugs in that version, for example, a non-quoted string that has a single quote in the value.
And I agree use the FileHelper library when you can, however that library requires you know what your data will look like... I need a generic parser.
So I've updated the code to the following and thought I'd share...
static public List<string> ParseDelimitedString(string value, char delimiter)
{
bool inQuotes = false;
bool inNonQuotes = false;
bool secondQuote = false;
char curQuote = '\0';
List<string> results = new List<string>();
StringBuilder sb = new StringBuilder();
foreach (char c in value)
{
if (inNonQuotes)
{
// then quotes are just characters
if (c == delimiter)
{
results.Add(sb.ToString());
sb.Remove(0, sb.Length);
inNonQuotes = false;
}
else
{
sb.Append(c);
}
}
else if (inQuotes)
{
// then quotes need to be double escaped
if ((c == '\'' && c == curQuote) || (c == '"' && c == curQuote))
{
if (secondQuote)
{
secondQuote = false;
sb.Append(c);
}
else
secondQuote = true;
}
else if (secondQuote && c == delimiter)
{
results.Add(sb.ToString());
sb.Remove(0, sb.Length);
inQuotes = false;
}
else if (!secondQuote)
{
sb.Append(c);
}
else
{
// bad,as,"user entered something like"this,poorly escaped,value
// just ignore until second delimiter found
}
}
else
{
// not yet parsing a field
if (c == '\'' || c == '"')
{
curQuote = c;
inQuotes = true;
inNonQuotes = false;
secondQuote = false;
}
else if (c == delimiter)
{
// blank field
inQuotes = false;
inNonQuotes = false;
results.Add(string.Empty);
}
else
{
inQuotes = false;
inNonQuotes = true;
sb.Append(c);
}
}
}
if (inQuotes || inNonQuotes)
results.Add(sb.ToString());
return results;
}
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