Group the collection using a function which returns the key. : ICollection « Collections Data Structure « C# / C Sharp

1. C# / C Sharp
2. Collections Data Structure
3. ICollection

Group the collection using a function which returns the key.

  

#region License
// Copyright 2006 James Newton-King
// http://www.newtonsoft.com
//
// This work is licensed under the Creative Commons Attribution 2.5 License
// http://creativecommons.org/licenses/by/2.5/
//
// You are free:
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//    * to make derivative works
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//
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//          - If you find this component useful a link to http://www.newtonsoft.com would be appreciated.
//    * For any reuse or distribution, you must make clear to others the license terms of this work.
//    * Any of these conditions can be waived if you get permission from the copyright holder.
#endregion

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

namespace MySpace.Common.IO.JSON.Utilities
{
    internal delegate T Func<A0, T>(A0 arg0);

    internal static class CollectionUtils
    {
        /// <summary>
        /// Group the collection using a function which returns the key.
        /// </summary>
        /// <param name="source">The source collection to group.</param>
        /// <param name="keySelector">The key selector.</param>
        /// <returns>A Dictionary with each key relating to a list of objects in a list grouped under it.</returns>
        public static Dictionary<K, List<V>> GroupBy<K, V>(ICollection<V> source, Func<V, K> keySelector)
        {
            if (keySelector == null)
                throw new ArgumentNullException("grouper");

            Dictionary<K, List<V>> groupedValues = new Dictionary<K, List<V>>();

            foreach (V value in source)
            {
                // using delegate to get the value's key
                K key = keySelector(value);
                List<V> groupedValueList;

                // add a list for grouped values if the key is not already in Dictionary
                if (!groupedValues.TryGetValue(key, out groupedValueList))
                {
                    groupedValueList = new List<V>();
                    groupedValues.Add(key, groupedValueList);
                }

                groupedValueList.Add(value);
            }

            return groupedValues;
        }
    }
}

   
    
  

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