MiniSet.cs

A Small Segmented Set Class

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
/// <summary>
/// Date: 10/03/20 **MJS**
/// Customer set using indexed hash buckets.
/// Possible uses less memory then standard hashset, with very similar search performance.
/// </summary>
/// <typeparam name="T"></typeparam>
[DebuggerDisplay("Count = {" + nameof(Count) + "}")]
[Serializable]
public class MiniSet<T> : IEnumerable<T>
{
    private  Bucket[]             _buckets;
    private  SizeHelper<T>        _newSize = new SizeHelper<T>();
    internal IEqualityComparer<T> Comparer;
    public   int                  Count;
    public   int                  ReSizes;
    public MiniSet(int size) : this(size, EqualityComparer<T>.Default)
    {
    }
    public MiniSet(int size, IEqualityComparer<T> comparer)
    {
        if (comparer == null)
            comparer = EqualityComparer<T>.Default;
        Comparer = comparer;
        _buckets = new Bucket[size];
        Count    = 0;
        ReSizes  = 0;
    }

    public MiniSet(IEnumerable<T> collection, IEqualityComparer<T> comparer)
    {
        if (comparer == null)
            comparer = EqualityComparer<T>.Default;
        Comparer = comparer;
        if (!(collection is ICollection<T> coll))
            return;
        Count    = coll.Count;
        _buckets = new Bucket[Count];
        UnionWith(coll);
    }
    public int                     ElementCount         => GetElementCount();
    public int                     NumberOfEmptyBuckets => GetNumberOfEmptyBuckets();
    public (int mDepth, int index) MaximumBucketDepth   => GetMaximumBucketDepth();
    public float                   LoadRatio            => GetLoadRatio();
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
    public void Clear()
    {
        _buckets.Clear();
    }
    public void UnionWith(IEnumerable<T> other)
    {
        if (other == null)
            throw new Exception("The other set must not be null.");
        foreach (var obj in other)
            Add(obj);
    }
    public bool Add(T item)
    {
        EnsureSize();
        var hashCode = Comparer.GetHashCode(item) & int.MaxValue;
        if (FindEntry(item, hashCode).APos != -1)
            return false;
        var pos = hashCode % _buckets.Length;
        if (_buckets[pos] == null)
            _buckets[pos] = new Bucket();
        _buckets[pos].Add(item);
        Count++;
        return true;
    }

    public int AddRange(IEnumerable<T> items)
    {
        return items.Sum(i => !Add(i) ? 0 : 1);
    }
    public T[] ToArray()
    {
        var newArray = new T[Count];
        using (var en = GetEnumerator())
        {
            var ptr = 0;
            while (en.MoveNext())
            {
                var value = en.Current;
                if (value == null)
                    break;
                newArray[ptr++] = value;
            }
            return newArray;
        }
    }
    private (int APos, int BPos) FindEntry(T item, int hashCode)
    {
        if (Count == 0)
            return (-1, -1);
        var aPos = hashCode % _buckets.Length;
        var bPos = 0;
        if (_buckets[aPos] == null)
            _buckets[aPos] = new Bucket();
        foreach (var i in _buckets[aPos].Values)
        {
            if (Comparer.Equals(i, item))
                return (aPos, bPos);
            bPos++;
        }
        return (-1, -1);
    }
    private void EnsureSize()
    {
        if (Count >= _buckets.Length)
        {
            ReSizes++;
            var cArray = ToArray();
            _buckets = new Bucket[_newSize.GetNewSize(_buckets.Length)];
            foreach (var i in cArray)
            {
                var hashCode = Comparer.GetHashCode(i) & int.MaxValue;
                var pos      = hashCode % _buckets.Length;
                if (_buckets[pos] == null)
                    _buckets[pos] = new Bucket();
                _buckets[pos].Add(i);
            }
        }
    }
    public bool Contains(T item)
    {
        var hashCode = Comparer.GetHashCode(item) & int.MaxValue;
        return FindEntry(item, hashCode).APos != -1;
    }
    public IEnumerator<T> GetEnumerator()
    {
        for (var i = 0; i < _buckets.Length; i++)
            if (_buckets[i] != null)
                for (var j = 0; j < _buckets[i].Count; ++j)
                    yield return _buckets[i].Values[j];
    }
    public int GetElementCount()
    {
        var count = 0;
        for (var i = 0; i < _buckets.Length; i++)
            if (_buckets[i] != null)
            {
                var c = _buckets[i].Count;
                count += c;
            }
        return count;
    }
    public int GetNumberOfEmptyBuckets()
    {
        var count = 0;
        for (var i = 0; i < _buckets.Length; i++)
            if (_buckets[i] == null)
                count++;
        return count;
    }
    public int GetNumberOfFilledBuckets()
    {
        var count = 0;
        for (var i = 0; i < _buckets.Length; i++)
            if (_buckets[i] != null)
                count++;
        return count;
    }
    public (int mDepth, int index) GetMaximumBucketDepth()
    {
        var max = 0;
        var j   = 0;
        for (var i = 0; i < _buckets.Length; i++)
            if (_buckets[i] != null)
            {
                var count = _buckets[i].Count;
                if (count > max)
                {
                    max = count;
                    j   = i;
                }
            }
        return (max, j);
    }
    public KeyValuePair<int, int>[] BucketDepthList => GetBucketDepthList();
    public KeyValuePair<int, int>[] GetBucketDepthList()
    {
        var bdic = new Dictionary<int, int>();
        for (var i = 0; i < _buckets.Length; i++)
            if (_buckets[i] != null)
            {
                var count = _buckets[i].Count;
                if (!bdic.ContainsKey(count))
                {
                    bdic.Add(count, 0);
                    bdic[count]++;
                }
                else
                {
                    bdic[count]++;
                }
            }
        return bdic.OrderByDescending(x=>x.Value).ToArray();
    }
    public float GetLoadRatio()
    {
        var x = Count;
        var y = _buckets.Length;
        var r = x / (float) y;
        return r;
    }
    internal class Bucket
    {
        public int Count;
        public T[] Values;
        public Bucket()
        {
            Values = new T[11];
            Count  = 0;
        }
        public void Add(T item)
        {
            if (Count >= Values.Length)
            {
                var ta = new T[Values.Length+3];
                Array.Copy(Values, 0, ta, 0, Count);
                Values = ta;
            }
            Values[Count++] = item;
        }
    }
}