/source/library/Interlace/Collections/EqualityPartitioner.cs

#region Using Directives and Copyright Notice



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using System;

using System.Collections.Generic;

using System.Text;



#endregion



namespace Interlace.Collections

{

    public class EqualityPartitioner<T>

    {

        public delegate object GetPropertyForEqualityRelation(T o);



        GetPropertyForEqualityRelation _propertyGetter;



        /// <summary>

        /// Initializes a new instance of the <see cref="T:EqualityPartitioner"/> class.

        /// </summary>

        /// <param name="relation">A function returning an object derived in some way from the

        /// objects being partitioned. The objects are partitioned based on equality of

        /// the derived object.</param>

        public EqualityPartitioner(GetPropertyForEqualityRelation propertyGetter)

        {

            _propertyGetter = propertyGetter;

        }



        public Set<Set<T>> Partition(ICollection<T> objects)

        {

            // A dictionary of the sets in the partition, keyed by some object in each set:

            Dictionary<object, Set<T>> partition = new Dictionary<object, Set<T>>();



            foreach (T candidate in objects)

            {

                object property = _propertyGetter(candidate);



                // First see if an existing set in the partition is suitable:

                if (!partition.ContainsKey(property))

                {

                    partition[property] = new Set<T>();

                }



                partition[property].UnionUpdate(candidate);

            }



            return new Set<Set<T>>(partition.Values);

        }

    }

}