parsing of a string containing an array

Question

I'd like to convert string containing recursive array of strings to an array of depth one.

Example:

StringToArray("[a, b, [c, [d, e]], f, [g, h], i]") == ["a", "b", "[c, [d, e]]", "f", "[g, h]", "i"]

Seems quite simple. But, I come from functional background and I'm not that familiar with .NET Framework standard libraries, so every time (I started from scratch like 3 times) I end up just plain ugly code. My latest implementation is here. As you see, it's ugly as hell.

So, what's the C# way to do this?

Answer 1

@ojlovecd has a good answer, using Regular Expressions.
However, his answer is overly complicated, so here's my similar, simpler answer.

public string[] StringToArray(string input) {
    var pattern = new Regex(@"
        \[
            (?:
            \s*
                (?<results>(?:
                (?(open)  [^\[\]]+  |  [^\[\],]+  )
                |(?<open>\[)
                |(?<-open>\])
                )+)
                (?(open)(?!))
            ,?
            )*
        \]
    ", RegexOptions.IgnorePatternWhitespace);

    // Find the first match:
    var result = pattern.Match(input);
    if (result.Success) {
        // Extract the captured values:
        var captures = result.Groups["results"].Captures.Cast<Capture>().Select(c => c.Value).ToArray();
        return captures;
    }
    // Not a match
    return null;
}

Using this code, you will see that StringToArray("[a, b, [c, [d, e]], f, [g, h], i]") will return the following array: ["a", "b", "[c, [d, e]]", "f", "[g, h]", "i"].

For more information on the balanced groups that I used for matching balanced braces, take a look at Microsoft's documentation.

Update:
As per the comments, if you want to also balance quotes, here's a possible modification. (Note that in C# the " is escaped as "") I also added descriptions of the pattern to help clarify it:

    var pattern = new Regex(@"
        \[
            (?:
            \s*
                (?<results>(?:              # Capture everything into 'results'
                    (?(open)                # If 'open' Then
                        [^\[\]]+            #   Capture everything but brackets
                        |                   # Else (not open):
                        (?:                 #   Capture either:
                            [^\[\],'""]+    #       Unimportant characters
                            |               #   Or
                            ['""][^'""]*?['""] #    Anything between quotes
                        )  
                    )                       # End If
                    |(?<open>\[)            # Open bracket
                    |(?<-open>\])           # Close bracket
                )+)
                (?(open)(?!))               # Fail while there's an unbalanced 'open'
            ,?
            )*
        \]
    ", RegexOptions.IgnorePatternWhitespace);

Answer 2

with Regex, it can solve your problem:

static string[] StringToArray(string str)
{
    Regex reg = new Regex(@"^\[(.*)\]$");
    Match match = reg.Match(str);
    if (!match.Success)
        return null;
    str = match.Groups[1].Value;
    List<string> list = new List<string>();
    reg = new Regex(@"\[[^\[\]]*(((?'Open'\[)[^\[\]]*)+((?'-Open'\])[^\[\]]*)+)*(?(Open)(?!))\]");
    Dictionary<string, string> dic = new Dictionary<string, string>();
    int index = 0;
    str = reg.Replace(str, m =>
    {
        string temp = "ojlovecd" + (index++).ToString();
        dic.Add(temp, m.Value);
        return temp;
    });
    string[] result = str.Split(',');
    for (int i = 0; i < result.Length; i++)
    {
        string s = result[i].Trim();
        if (dic.ContainsKey(s))
            result[i] = dic[s].Trim();
        else
            result[i] = s;
    }
    return result;
}

Answer 3

Honestly I would just write this method in an F# assembly as its probably much easier. If you look at the JavaScriptSerializer implementation in C# (with a decompiler like dotPeek or reflector) you can see how messy the array parsing code is for a similar array in JSON. Granted this has to handle a much more varied array of tokens, but you get the idea.

Here is their DeserializeList implementation, uglier than it is normally as its dotPeek's decompiled version, not the original, but you get the idea. The DeserializeInternal would recurse down to the child list.

private IList DeserializeList(int depth)
{
  IList list = (IList) new ArrayList();
  char? nullable1 = this._s.MoveNext();
  if (((int) nullable1.GetValueOrDefault() != 91 ? 1 : (!nullable1.HasValue ? 1 : 0)) != 0)
    throw new ArgumentException(this._s.GetDebugString(AtlasWeb.JSON_InvalidArrayStart));
  bool flag = false;
  char? nextNonEmptyChar;
  char? nullable2;
  do
  {
    char? nullable3 = nextNonEmptyChar = this._s.GetNextNonEmptyChar();
    if ((nullable3.HasValue ? new int?((int) nullable3.GetValueOrDefault()) : new int?()).HasValue)
    {
      char? nullable4 = nextNonEmptyChar;
      if (((int) nullable4.GetValueOrDefault() != 93 ? 1 : (!nullable4.HasValue ? 1 : 0)) != 0)
      {
        this._s.MovePrev();
        object obj = this.DeserializeInternal(depth);
        list.Add(obj);
        flag = false;
        nextNonEmptyChar = this._s.GetNextNonEmptyChar();
        char? nullable5 = nextNonEmptyChar;
        if (((int) nullable5.GetValueOrDefault() != 93 ? 0 : (nullable5.HasValue ? 1 : 0)) == 0)
        {
          flag = true;
          nullable2 = nextNonEmptyChar;
        }
        else
          goto label_8;
      }
      else
        goto label_8;
    }
    else
      goto label_8;
  }
  while (((int) nullable2.GetValueOrDefault() != 44 ? 1 : (!nullable2.HasValue ? 1 : 0)) == 0);
  throw new ArgumentException(this._s.GetDebugString(AtlasWeb.JSON_InvalidArrayExpectComma));
 label_8:
  if (flag)
    throw new ArgumentException(this._s.GetDebugString(AtlasWeb.JSON_InvalidArrayExtraComma));
  char? nullable6 = nextNonEmptyChar;
  if (((int) nullable6.GetValueOrDefault() != 93 ? 1 : (!nullable6.HasValue ? 1 : 0)) != 0)
    throw new ArgumentException(this._s.GetDebugString(AtlasWeb.JSON_InvalidArrayEnd));
  else
    return list;
}

Recursive parsing is just not managed as well though in C# as it is in F#.

Answer 4

There is no real "standard" way of doing this. Note that the implementation can get pretty messy if you want to consider all possibilities. I would recommend something recursive like:

    private static IEnumerable<object> StringToArray2(string input)
    {
        var characters = input.GetEnumerator();
        return InternalStringToArray2(characters);
    }

    private static IEnumerable<object> InternalStringToArray2(IEnumerator<char> characters)
    {
        StringBuilder valueBuilder = new StringBuilder();

        while (characters.MoveNext())
        {
            char current = characters.Current;

            switch (current)
            {
                case '[':
                    yield return InternalStringToArray2(characters);
                    break;
                case ']':
                    yield return valueBuilder.ToString();
                    valueBuilder.Clear();
                    yield break;
                case ',':
                    yield return valueBuilder.ToString();
                    valueBuilder.Clear();
                    break;
                default:
                    valueBuilder.Append(current);
                    break;
            }

Although your not restricted to recursiveness and can always fall back to a single method like

    private static IEnumerable<object> StringToArray1(string input)
    {
        Stack<List<object>> levelEntries = new Stack<List<object>>();
        List<object> current = null;
        StringBuilder currentLineBuilder = new StringBuilder();

        foreach (char nextChar in input)
        {
            switch (nextChar)
            {
                case '[':
                    levelEntries.Push(current);
                    current = new List<object>();
                    break;
                case ']':
                    current.Add(currentLineBuilder.ToString());
                    currentLineBuilder.Clear();
                    var last = current;
                    if (levelEntries.Peek() != null)
                    {
                        current = levelEntries.Pop();
                        current.Add(last);
                    }
                    break;
                case ',':
                    current.Add(currentLineBuilder.ToString());
                    currentLineBuilder.Clear();
                    break;
                default:
                    currentLineBuilder.Append(nextChar);
                    break;
            }
        }

        return current;
    }

Whatever smells good to you

Answer 5

using System;
using System.Text;
using System.Text.RegularExpressions;
using Microsoft.VisualBasic.FileIO; //Microsoft.VisualBasic.dll
using System.IO;

public class Sample {
    static void Main(){
        string data = "[a, b, [c, [d, e]], f, [g, h], i]";
        string[] fields = StringToArray(data);
        //check print
        foreach(var item in fields){
            Console.WriteLine("\"{0}\"",item);
        }
    }
    static string[] StringToArray(string data){
        string[] fields = null;
        Regex innerPat = new Regex(@"\[\s*(.+)\s*\]");
        string innerStr = innerPat.Matches(data)[0].Groups[1].Value;
        StringBuilder wk = new StringBuilder();
        var balance = 0;
        for(var i = 0;i<innerStr.Length;++i){
            char ch = innerStr[i];
            switch(ch){
            case '[':
                if(balance == 0){
                    wk.Append('"');
                }
                wk.Append(ch);
                ++balance;
                continue;
            case ']':
                wk.Append(ch);
                --balance;
                if(balance == 0){
                    wk.Append('"');
                }
                continue;
            default:
                wk.Append(ch);
                break;
            }
        }
        var reader = new StringReader(wk.ToString());
        using(var csvReader = new TextFieldParser(reader)){
            csvReader.SetDelimiters(new string[] {","});
            csvReader.HasFieldsEnclosedInQuotes = true;
            fields = csvReader.ReadFields();
        }
        return fields;
    }
}