LINQ approach to flatten Dictionary to string

Question

I have a Dictionary<string,string> and want to flatten it out with this pattern:

{key}={value}|{key}={value}|{key}={value}|

I tried with a LINQ approach at first but couldn't solve it, so I ended up writing an extension method like this:

public static string ToString(this Dictionary<string,string> source, string keyValueSeparator, string sequenceSeparator)
{
  if (source == null)
    throw new ArgumentException("Parameter source can not be null.");

  var str = new StringBuilder();
  foreach (var keyvaluepair in source)
    str.Append(string.Format("{0}{1}{2}{3}", keyvaluepair.Key, keyValueSeparator, keyvaluepair.Value, sequenceSeparator));
  var retval = str.ToString();
  return retval.Substring(0,retval.Length - sequenceSeparator.Length); //remove last  seq_separator
}

Is it possible to solve this with LINQ?

Answer 1

Something like this should work:

public static string ToString(this Dictionary<string,string> source, string keyValueSeparator, string sequenceSeparator)
{
  if (source == null)
    throw new ArgumentException("Parameter source can not be null.");

  var pairs = source.Select(x => string.Format("{0}{1}{2}", x.Key, keyValueSeparator, x.Value));

  return string.Join(sequenceSeparator, pairs);
}

Answer 2

You can actually inline all this with the Aggregate method from LINQ.

return d.Aggregate(new StringBuilder(), (sb, x) => sb.Append(x.Key + keySep + x.Value + pairSep), sb => sb.ToString(0, sb.Length - 1));

Assuming you can read LINQ, it is probably the cleanest. But it isn't the fastest. I tried all the proposed solutions, and the answer by Mattias is actually the fastest proposed so far.

I have one that is faster though.

StringBuilder sb = new StringBuilder();
foreach (var x in d)
{
    sb.Append(x.Key);
    sb.Append(keySep);
    sb.Append(x.Value);
    sb.Append(pairSep);
}

return sb.ToString(0, sb.Length - 1);

It is faster to call Append multiple times, and it is also faster to run it expanded like this rather than in my Aggregate (changed to do multiple appends).

Of course the performance difference between all of these is negligible. So choose the one that reads the clearest to you and will be best understood by someone else looking at the code.

Answer 3

Chris Sainty's answer is probably the fastest, but here's the shortest - using Linq as requested:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public static class DictionaryExtension 
{ 
    public static string ToStringFlattened(this Dictionary<string, string> source, string keyValueSeparator="=", char sequenceSeparator='|')
    {
        return source == null ? 
                           "" : source.Aggregate("", (str, v) => 
                                         str + v.Key 
                                             +  keyValueSeparator 
                                             + v.Value 
                                             + sequenceSeparator)
                                      .TrimEnd(sequenceSeparator);
    }
}

static void Main()
{
    Console.WriteLine(
      new Dictionary<string, string>() 
        { { "key1", "val1" }, { "key2", "value2" }, }.ToStringFlattened()
    );
}

In .Net Framework >= 4.0 you can just use Zip:

public static string ToStringFlattened(this Dictionary<string, string> source, string keyValueSeparator="=", string sequenceSeparator="|")
{
    return source == null ? "" : string.Join(sequenceSeparator, source.Keys.Zip(source.Values, (k, v) => k + keyValueSeparator + v));
}

Note: If you want to keep the sequenceSeparator at the end, remove the Trim from the first method, and add ('+') the sequenceSeparator to the return value of the second example.

Answer 4

Do you need it as a string in particular or just want to store a dictionary as a setting in the "Application Settings" section of the project properties? If you simply need to store a dictionary in the settings file, the following code may suit your needs as well:

public static string Serialize(object obj)
    {
        MemoryStream memorystream = new MemoryStream();
        BinaryFormatter bf = new BinaryFormatter();
        bf.Serialize(memorystream, obj);
        byte[] mStream = memorystream.ToArray();
        string slist = Convert.ToBase64String(mStream);
        return slist;
    }

public static object Unserialize(string str)
    {
        byte[] mData = Convert.FromBase64String(str);
        MemoryStream memorystream = new MemoryStream(mData);
        BinaryFormatter bf = new BinaryFormatter();
        Object obj = bf.Deserialize(memorystream);
        return obj;
    }

Pass your dictionary (or list, queue, stack, whatever) to Serialize and the function returns a string representing that object, like this:

 string mystr = Serialize(mydict);

To return the object from the string created by the Serialize function, pass that string to Unserialize and it will return an object. You will need to cast back to your original type, such as:

 Dictionary<string,string> mydict = (Dictionary<string,string>)Unserialize(string mystr);

Answer 5

How about this?

Firstly, if you haven't already created the ForEach extension method, add one:

public static class EnumerableExtensions
{
    public static void ForEach<T>(this IEnumerable<T> items, Action<T> action)
    {
        foreach (var item in items)
        {
            action(item);
        }
    }
}

Then add an extension method for your dictionary:

public static class DictionaryExtensions
{
    public static string ToString<TKey, TValue>(
        this IDictionary<TKey, TValue> dictionary, string keyValueSeparator, string sequenceSeparator)
    {
        var stringBuilder = new StringBuilder();
        dictionary.ForEach(
            x => stringBuilder.AppendFormat("{0}{1}{2}{3}", x.Key.ToString(), keyValueSeparator, x.Value.ToString(), sequenceSeparator));

        return stringBuilder.ToString(0, stringBuilder.Length - sequenceSeparator.Length);
    }
}

Then to call it:

var dictionary = new Dictionary<string, string>();
dictionary.Add("key1", "value1");
dictionary.Add("key2", "value2");
dictionary.Add("key3", "value3");

System.Console.WriteLine(dictionary.ToString("=", "|"));

Answer 6

Pure LINQ way using StringBuilder is also possible:

    public static string ToStringLinq<TKey, TValue>(this Dictionary<TKey, TValue> source, string keyValueSeparator, string sequenceSeparator)
    {
        return source.Aggregate(new StringBuilder(),
            (acc, pair) => acc.AppendFormat("{0}{1}{2}{3}", pair.Key, keyValueSeparator, pair.Value, sequenceSeparator),
            builder => builder.Length > sequenceSeparator.Length ?
                builder.ToString(0, builder.Length - sequenceSeparator.Length)
                : String.Empty
            );
    }

Answer 7

The pure LINQ way of doing it is with the Aggregate extension method:

public static string ToStringLinq<TKey, TValue> (this Dictionary<TKey, TValue> source, string keyValueSeparator, string sequenceSeparator)
{
    return source.Aggregate(string.Empty, (acc, pair) => string.Format("{0}{1}{2}{3}{4}", acc, sequenceSeparator, pair.Key, keyValueSeparator, pair.Value));
}

The downside of the above method is that it will put a sequence separator at the start of your string.

Alternatively:

public static string ToStringLinq<TKey, TValue> (this Dictionary<TKey, TValue> source, string keyValueSeparator, string sequenceSeparator)
{
    return source.Aggregate(string.Empty, (acc, pair) => string.Format("{0}{1}{2}{3}{4}", acc, pair.Key, keyValueSeparator, pair.Value, sequenceSeparator));
}

This will place a separator at the end instead of the beginning.

If it is important not to have a leading or trailing separator, you can certainly update the lambda to account for a case with an empty accumulator, or you could add code to seed with a string for the first element and then aggregate over the rest of the dictionary, as shown below:

public static string ToStringLinq<TKey, TValue> (this Dictionary<TKey, TValue> source, string keyValueSeparator, string sequenceSeparator)
{
    var first = source.First();
    var seed = string.Format("{0}{1}{2}", first.Key, keyValueSeparator, first.Value);

    return source.Skip(1).Aggregate(seed, (acc, pair) => string.Format("{0}{1}{2}{3}{4}", acc, sequenceSeparator, pair.Key, keyValueSeparator, pair.Value));
}

Of course, this suffers the same problem of Mattias' answer, where it does more object creation as a result of the repeat string.Format calls, but for situations where performance is not an issue, a single aggregate function call can be a very compact means of solving the problem.

Answer 8

From Mattias solution:

• string.Concat() is faster then string.Format()
• No need to build up an array before string.Join()

public static string ToString(this Dictionary<string,string> source, string keyValueSeparator, string sequenceSeparator)
{
    if (source == null) throw new ArgumentException("Parameter source can not be null.");

    var pairs = source.Select(x => string.Concat(x.Key, keyValueSeparator, x.Value));

    return string.Join(sequenceSeparator, pairs);
}