source: branches/GP.Grammar.Editor/HeuristicLab.Encodings.SymbolicExpressionTreeEncoding/3.4/SymbolicExpressionGrammarBase.cs @ 6387

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2011 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
 *
 * This file is part of HeuristicLab.
 *
 * HeuristicLab is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * HeuristicLab is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
 */
#endregion

using System;
using System.Collections.Generic;
using System.Linq;
using HeuristicLab.Collections;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;

namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
  /// <summary>
  /// The default symbolic expression grammar stores symbols and syntactic constraints for symbols.
  /// Symbols are treated as equvivalent if they have the same name.
  /// Syntactic constraints limit the number of allowed sub trees for a node with a symbol and which symbols are allowed 
  /// in the sub-trees of a symbol (can be specified for each sub-tree index separately).
  /// </summary>
  [StorableClass]
  public abstract class SymbolicExpressionGrammarBase : NamedItem, ISymbolicExpressionGrammarBase {

    #region properties for separation between implementation and persistence
    [Storable(Name = "Symbols")]
    private IEnumerable<ISymbol> StorableSymbols {
      get { return symbols.Values.ToArray(); }
      set { symbols = value.ToDictionary(sym => sym.Name); }
    }

    [Storable(Name = "SymbolSubtreeCount")]
    private IEnumerable<KeyValuePair<ISymbol, Tuple<int, int>>> StorableSymbolSubtreeCount {
      get { return symbolSubtreeCount.Select(x => new KeyValuePair<ISymbol, Tuple<int, int>>(GetSymbol(x.Key), x.Value)).ToArray(); }
      set { symbolSubtreeCount = value.ToDictionary(x => x.Key.Name, x => x.Value); }
    }

    [Storable(Name = "AllowedChildSymbols")]
    private IEnumerable<KeyValuePair<ISymbol, IEnumerable<ISymbol>>> StorableAllowedChildSymbols {
      get { return allowedChildSymbols.Select(x => new KeyValuePair<ISymbol, IEnumerable<ISymbol>>(GetSymbol(x.Key), x.Value.Select(y => GetSymbol(y)).ToArray())).ToArray(); }
      set { allowedChildSymbols = value.ToDictionary(x => x.Key.Name, x => x.Value.Select(y => y.Name).ToList()); }
    }

    [Storable(Name = "AllowedChildSymbolsPerIndex")]
    private IEnumerable<KeyValuePair<Tuple<ISymbol, int>, IEnumerable<ISymbol>>> StorableAllowedChildSymbolsPerIndex {
      get { return allowedChildSymbolsPerIndex.Select(x => new KeyValuePair<Tuple<ISymbol, int>, IEnumerable<ISymbol>>(Tuple.Create<ISymbol, int>(GetSymbol(x.Key.Item1), x.Key.Item2), x.Value.Select(y => GetSymbol(y)).ToArray())).ToArray(); }
      set { allowedChildSymbolsPerIndex = value.ToDictionary(x => Tuple.Create(x.Key.Item1.Name, x.Key.Item2), x => x.Value.Select(y => y.Name).ToList()); }
    }
    #endregion

    protected bool suppressEvents;
    protected Dictionary<string, ISymbol> symbols;
    protected Dictionary<string, Tuple<int, int>> symbolSubtreeCount;
    protected Dictionary<string, List<string>> allowedChildSymbols;
    protected Dictionary<Tuple<string, int>, List<string>> allowedChildSymbolsPerIndex;

    public override bool CanChangeName {
      get { return false; }
    }
    public override bool CanChangeDescription {
      get { return false; }
    }

    [StorableConstructor]
    protected SymbolicExpressionGrammarBase(bool deserializing)
      : base(deserializing) {
      cachedMinExpressionLength = new Dictionary<string, int>();
      cachedMaxExpressionLength = new Dictionary<string, int>();
      cachedMinExpressionDepth = new Dictionary<string, int>();

      suppressEvents = false;
    }
    [StorableHook(HookType.AfterDeserialization)]
    private void AfterDeserialization() {
      foreach (ISymbol symbol in symbols.Values)
        RegisterSymbolEvents(symbol);
    }

    protected SymbolicExpressionGrammarBase(SymbolicExpressionGrammarBase original, Cloner cloner)
      : base(original, cloner) {
      cachedMinExpressionLength = new Dictionary<string, int>();
      cachedMaxExpressionLength = new Dictionary<string, int>();
      cachedMinExpressionDepth = new Dictionary<string, int>();

      symbols = original.symbols.ToDictionary(x => x.Key, y => (ISymbol)cloner.Clone(y.Value));
      symbolSubtreeCount = new Dictionary<string, Tuple<int, int>>(original.symbolSubtreeCount);

      allowedChildSymbols = new Dictionary<string, List<string>>();
      foreach (var element in original.allowedChildSymbols)
        allowedChildSymbols.Add(element.Key, new List<string>(element.Value));

      allowedChildSymbolsPerIndex = new Dictionary<Tuple<string, int>, List<string>>();
      foreach (var element in original.allowedChildSymbolsPerIndex)
        allowedChildSymbolsPerIndex.Add(element.Key, new List<string>(element.Value));

      foreach (ISymbol symbol in symbols.Values)
        RegisterSymbolEvents(symbol);

      suppressEvents = false;
    }

    protected SymbolicExpressionGrammarBase(string name, string description)
      : base(name, description) {
      cachedMinExpressionLength = new Dictionary<string, int>();
      cachedMaxExpressionLength = new Dictionary<string, int>();
      cachedMinExpressionDepth = new Dictionary<string, int>();

      symbols = new Dictionary<string, ISymbol>();
      symbolSubtreeCount = new Dictionary<string, Tuple<int, int>>();
      allowedChildSymbols = new Dictionary<string, List<string>>();
      allowedChildSymbolsPerIndex = new Dictionary<Tuple<string, int>, List<string>>();

      suppressEvents = false;
    }

    #region protected grammar manipulation methods
    protected void AddSymbol(ISymbol symbol) {
      AddSymbolToDictionaries(symbol);
      var groupSymbol = symbol as GroupSymbol;
      if (groupSymbol != null) {
        foreach (ISymbol s in groupSymbol.Flatten())
          AddSymbolToDictionaries(s);
      }

      ClearCaches();
      OnChanged();
    }
    private void AddSymbolToDictionaries(ISymbol symbol) {
      symbols.Add(symbol.Name, symbol);
      symbolSubtreeCount.Add(symbol.Name, Tuple.Create(symbol.MinimumArity, symbol.MaximumArity));
      RegisterSymbolEvents(symbol);
    }

    protected void RemoveSymbol(ISymbol symbol) {
      RemoveSymbolFromDictionaries(symbol);
      var groupSymbol = symbol as GroupSymbol;
      if (groupSymbol != null) {
        foreach (ISymbol s in groupSymbol.Flatten())
          RemoveSymbolFromDictionaries(s);
      }

      foreach (GroupSymbol group in symbols.Values.OfType<GroupSymbol>())
        group.SymbolsCollection.Remove(symbol);

      ClearCaches();
      OnChanged();
    }
    private void RemoveSymbolFromDictionaries(ISymbol symbol) {
      symbols.Remove(symbol.Name);
      allowedChildSymbols.Remove(symbol.Name);
      for (int i = 0; i < GetMaximumSubtreeCount(symbol); i++)
        allowedChildSymbolsPerIndex.Remove(Tuple.Create(symbol.Name, i));
      symbolSubtreeCount.Remove(symbol.Name);

      foreach (var parent in Symbols) {
        List<string> allowedChilds;
        if (allowedChildSymbols.TryGetValue(parent.Name, out allowedChilds))
          allowedChilds.Remove(symbol.Name);

        for (int i = 0; i < GetMaximumSubtreeCount(parent); i++) {
          if (allowedChildSymbolsPerIndex.TryGetValue(Tuple.Create(parent.Name, i), out allowedChilds))
            allowedChilds.Remove(symbol.Name);
        }
      }
      DeregisterSymbolEvents(symbol);
    }

    public virtual ISymbol GetSymbol(string symbolName) {
      ISymbol symbol;
      if (symbols.TryGetValue(symbolName, out symbol)) return symbol;
      return null;
    }

    protected void AddAllowedChildSymbol(ISymbol parent, ISymbol child) {
      List<ISymbol> parents;
      List<ISymbol> childs;
      bool changed = false;

      var parentGroup = parent as GroupSymbol;
      if (parentGroup != null) parents = parentGroup.Flatten().Where(p => !(p is GroupSymbol)).ToList();
      else parents = new List<ISymbol>() { parent };
      var childGroup = child as GroupSymbol;
      if (childGroup != null) childs = childGroup.Flatten().Where(c => !(c is GroupSymbol)).ToList();
      else childs = new List<ISymbol>() { child };

      foreach (ISymbol p in parents) {
        foreach (ISymbol c in childs) {
          changed |= AddAllowedChildSymbolToDictionaries(p, c);
        }
      }

      if (changed) {
        ClearCaches();
        OnChanged();
      }
    }

    private bool AddAllowedChildSymbolToDictionaries(ISymbol parent, ISymbol child) {
      List<string> childSymbols;
      if (!allowedChildSymbols.TryGetValue(parent.Name, out childSymbols)) {
        childSymbols = new List<string>();
        allowedChildSymbols.Add(parent.Name, childSymbols);
      }
      if (childSymbols.Contains(child.Name)) return false;

      suppressEvents = true;
      for (int argumentIndex = 0; argumentIndex < GetMaximumSubtreeCount(parent); argumentIndex++)
        RemoveAllowedChildSymbol(parent, child, argumentIndex);
      suppressEvents = false;

      childSymbols.Add(child.Name);
      return true;
    }

    protected void AddAllowedChildSymbol(ISymbol parent, ISymbol child, int argumentIndex) {
      List<ISymbol> parents;
      List<ISymbol> childs;
      bool changed = false;

      var parentGroup = parent as GroupSymbol;
      if (parentGroup != null) parents = parentGroup.Flatten().Where(p => !(p is GroupSymbol)).ToList();
      else parents = new List<ISymbol>() { parent };
      var childGroup = child as GroupSymbol;
      if (childGroup != null) childs = childGroup.Flatten().Where(c => !(c is GroupSymbol)).ToList();
      else childs = new List<ISymbol>() { child };

      foreach (ISymbol p in parents) {
        foreach (ISymbol c in childs) {
          changed |= AddAllowedChildSymbolToDictionaries(p, c, argumentIndex);
        }
      }

      if (changed) {
        ClearCaches();
        OnChanged();
      }
    }


    private bool AddAllowedChildSymbolToDictionaries(ISymbol parent, ISymbol child, int argumentIndex) {
      List<string> childSymbols;
      if (allowedChildSymbols.TryGetValue(parent.Name, out childSymbols))
        if (childSymbols.Contains(child.Name)) return false;

      var key = Tuple.Create(parent.Name, argumentIndex);
      if (!allowedChildSymbolsPerIndex.TryGetValue(key, out childSymbols)) {
        childSymbols = new List<string>();
        allowedChildSymbolsPerIndex.Add(key, childSymbols);
      }
      if (childSymbols.Contains(child.Name)) return false;

      childSymbols.Add(child.Name);
      return true;
    }

    protected void RemoveAllowedChildSymbol(ISymbol parent, ISymbol child) {
      bool changed = false;
      List<string> childSymbols;
      if (allowedChildSymbols.TryGetValue(child.Name, out childSymbols)) {
        changed |= childSymbols.Remove(child.Name);
      }

      for (int argumentIndex = 0; argumentIndex < GetMaximumSubtreeCount(parent); argumentIndex++) {
        var key = Tuple.Create(parent.Name, argumentIndex);
        if (allowedChildSymbolsPerIndex.TryGetValue(key, out childSymbols))
          changed |= childSymbols.Remove(child.Name);
      }

      if (changed) {
        ClearCaches();
        OnChanged();
      }
    }

    protected void RemoveAllowedChildSymbol(ISymbol parent, ISymbol child, int argumentIndex) {
      bool changed = false;

      suppressEvents = true;
      List<string> childSymbols;
      if (allowedChildSymbols.TryGetValue(parent.Name, out childSymbols)) {
        if (childSymbols.Remove(child.Name)) {
          for (int i = 0; i < GetMaximumSubtreeCount(parent); i++) {
            if (i != argumentIndex) AddAllowedChildSymbol(parent, child, i);
          }
          changed = true;
        }
      }
      suppressEvents = false;

      var key = Tuple.Create(parent.Name, argumentIndex);
      if (allowedChildSymbolsPerIndex.TryGetValue(key, out childSymbols))
        changed |= childSymbols.Remove(child.Name);

      if (changed) {
        ClearCaches();
        OnChanged();
      }
    }

    protected void SetSubtreeCount(ISymbol symbol, int minimumSubtreeCount, int maximumSubtreeCount) {
      var groupSymbol = symbol as GroupSymbol;
      if (groupSymbol != null) {
        var symbols = groupSymbol.Flatten().Where(s => !(s is GroupSymbol));
        if (symbols.Any(s => s.MinimumArity > minimumSubtreeCount)) throw new ArgumentException("Invalid minimum subtree count " + minimumSubtreeCount + " for " + symbol);
        if (symbols.Any(s => s.MaximumArity < maximumSubtreeCount)) throw new ArgumentException("Invalid minimum subtree count " + minimumSubtreeCount + " for " + symbol);
        foreach (ISymbol s in symbols)
          SetSubTreeCountInDictionaries(s, minimumSubtreeCount, maximumSubtreeCount);
      } else {
        if (symbol.MinimumArity > minimumSubtreeCount) throw new ArgumentException("Invalid minimum subtree count " + minimumSubtreeCount + " for " + symbol);
        if (symbol.MaximumArity < maximumSubtreeCount) throw new ArgumentException("Invalid minimum subtree count " + minimumSubtreeCount + " for " + symbol);
        SetSubTreeCountInDictionaries(symbol, minimumSubtreeCount, maximumSubtreeCount);
      }

      ClearCaches();
      OnChanged();
    }

    private void SetSubTreeCountInDictionaries(ISymbol symbol, int minimumSubtreeCount, int maximumSubtreeCount) {
      for (int i = GetMaximumSubtreeCount(symbol) - 1; i >= maximumSubtreeCount; i--) {
        var key = Tuple.Create(symbol.Name, i);
        allowedChildSymbolsPerIndex.Remove(key);
      }

      symbolSubtreeCount[symbol.Name] = Tuple.Create(minimumSubtreeCount, maximumSubtreeCount);
    }
    #endregion

    public virtual IEnumerable<ISymbol> Symbols {
      get { return symbols.Values; }
    }
    public virtual IEnumerable<ISymbol> AllowedSymbols {
      get { return Symbols.Where(s => s.Enabled); }
    }
    public virtual bool ContainsSymbol(ISymbol symbol) {
      return symbols.ContainsKey(symbol.Name);
    }

    public virtual bool IsAllowedChildSymbol(ISymbol parent, ISymbol child) {
      if (!child.Enabled) return false;

      List<string> temp;
      if (allowedChildSymbols.TryGetValue(parent.Name, out temp))
        return temp.Contains(child.Name);
      return false;
    }

    public virtual bool IsAllowedChildSymbol(ISymbol parent, ISymbol child, int argumentIndex) {
      if (!child.Enabled) return false;

      List<string> temp;
      if (allowedChildSymbols.TryGetValue(parent.Name, out temp))
        if (temp.Contains(child.Name)) return true;

      var key = Tuple.Create(parent.Name, argumentIndex);
      if (allowedChildSymbolsPerIndex.TryGetValue(key, out temp))
        return temp.Contains(child.Name);
      return false;
    }

    public virtual IEnumerable<ISymbol> GetAllowedChildSymbols(ISymbol parent) {
      List<string> childs;
      if (allowedChildSymbols.TryGetValue(parent.Name, out childs))
        return childs.Select(s => GetSymbol(s)).Where(s => s.Enabled);
      return Enumerable.Empty<ISymbol>();
    }

    public virtual IEnumerable<ISymbol> GetAllowedChildSymbols(ISymbol parent, int argumentIndex) {
      var result = Enumerable.Empty<string>();

      List<string> temp;
      if (allowedChildSymbols.TryGetValue(parent.Name, out temp))
        result = result.Union(temp);
      var key = Tuple.Create(parent.Name, argumentIndex);
      if (allowedChildSymbolsPerIndex.TryGetValue(key, out temp))
        result = result.Union(temp);

      return result.Select(x => GetSymbol(x)).Where(s => s.Enabled);
    }

    public virtual int GetMinimumSubtreeCount(ISymbol symbol) {
      return symbolSubtreeCount[symbol.Name].Item1;
    }
    public virtual int GetMaximumSubtreeCount(ISymbol symbol) {
      return symbolSubtreeCount[symbol.Name].Item2;
    }

    private void ClearCaches() {
      cachedMinExpressionLength.Clear();
      cachedMaxExpressionLength.Clear();
      cachedMinExpressionDepth.Clear();
    }

    private Dictionary<string, int> cachedMinExpressionLength;
    public int GetMinimumExpressionLength(ISymbol symbol) {
      int temp;
      if (!cachedMinExpressionLength.TryGetValue(symbol.Name, out temp)) {
        cachedMinExpressionLength[symbol.Name] = int.MaxValue; // prevent infinite recursion
        long sumOfMinExpressionLengths = 1 + (from argIndex in Enumerable.Range(0, GetMinimumSubtreeCount(symbol))
                                              let minForSlot = (long)(from s in GetAllowedChildSymbols(symbol, argIndex)
                                                                      select GetMinimumExpressionLength(s)).DefaultIfEmpty(0).Min()
                                              select minForSlot).DefaultIfEmpty(0).Sum();

        cachedMinExpressionLength[symbol.Name] = (int)Math.Min(sumOfMinExpressionLengths, int.MaxValue);
        return cachedMinExpressionLength[symbol.Name];
      }
      return temp;
    }

    private Dictionary<string, int> cachedMaxExpressionLength;
    public int GetMaximumExpressionLength(ISymbol symbol) {
      int temp;
      if (!cachedMaxExpressionLength.TryGetValue(symbol.Name, out temp)) {
        cachedMaxExpressionLength[symbol.Name] = int.MaxValue; // prevent infinite recursion
        long sumOfMaxTrees = 1 + (from argIndex in Enumerable.Range(0, GetMaximumSubtreeCount(symbol))
                                  let maxForSlot = (long)(from s in GetAllowedChildSymbols(symbol, argIndex)
                                                          select GetMaximumExpressionLength(s)).DefaultIfEmpty(0).Max()
                                  select maxForSlot).DefaultIfEmpty(0).Sum();
        cachedMaxExpressionLength[symbol.Name] = (int)Math.Min(sumOfMaxTrees, int.MaxValue);
        return cachedMaxExpressionLength[symbol.Name];
      }
      return temp;
    }

    private Dictionary<string, int> cachedMinExpressionDepth;
    public int GetMinimumExpressionDepth(ISymbol symbol) {
      int temp;
      if (!cachedMinExpressionDepth.TryGetValue(symbol.Name, out temp)) {
        cachedMinExpressionDepth[symbol.Name] = int.MaxValue; // prevent infinite recursion
        long minDepth = 1 + (from argIndex in Enumerable.Range(0, GetMinimumSubtreeCount(symbol))
                             let minForSlot = (long)(from s in GetAllowedChildSymbols(symbol, argIndex)
                                                     select GetMinimumExpressionDepth(s)).DefaultIfEmpty(0).Min()
                             select minForSlot).DefaultIfEmpty(0).Max();
        cachedMinExpressionDepth[symbol.Name] = (int)Math.Min(minDepth, int.MaxValue);
        return cachedMinExpressionDepth[symbol.Name];
      }
      return temp;
    }


    #region events
    private void RegisterSymbolEvents(ISymbol symbol) {
      symbol.NameChanging += new EventHandler<CancelEventArgs<string>>(Symbol_NameChanging);
      symbol.NameChanged += new EventHandler(Symbol_NameChanged);
      symbol.Changed += new EventHandler(Symbol_Changed);
      var groupSymbol = symbol as GroupSymbol;
      if (groupSymbol != null) RegisterGroupSymbolEvents(groupSymbol);
    }
    private void DeregisterSymbolEvents(ISymbol symbol) {
      symbol.NameChanging -= new EventHandler<CancelEventArgs<string>>(Symbol_NameChanging);
      symbol.NameChanged -= new EventHandler(Symbol_NameChanged);
      symbol.Changed -= new EventHandler(Symbol_Changed);
      var groupSymbol = symbol as GroupSymbol;
      if (groupSymbol != null) DeregisterGroupSymbolEvents(groupSymbol);
    }

    private void RegisterGroupSymbolEvents(GroupSymbol groupSymbol) {
      groupSymbol.SymbolsCollection.ItemsAdded += new Collections.CollectionItemsChangedEventHandler<ISymbol>(GroupSymbol_ItemsAdded);
      groupSymbol.SymbolsCollection.ItemsRemoved += new Collections.CollectionItemsChangedEventHandler<ISymbol>(GroupSymbol_ItemsRemoved);
      groupSymbol.SymbolsCollection.CollectionReset += new Collections.CollectionItemsChangedEventHandler<ISymbol>(GroupSymbol_CollectionReset);
    }
    private void DeregisterGroupSymbolEvents(GroupSymbol groupSymbol) {
      groupSymbol.SymbolsCollection.ItemsAdded -= new Collections.CollectionItemsChangedEventHandler<ISymbol>(GroupSymbol_ItemsAdded);
      groupSymbol.SymbolsCollection.ItemsRemoved -= new Collections.CollectionItemsChangedEventHandler<ISymbol>(GroupSymbol_ItemsRemoved);
      groupSymbol.SymbolsCollection.CollectionReset -= new Collections.CollectionItemsChangedEventHandler<ISymbol>(GroupSymbol_CollectionReset);
    }

    private void Symbol_NameChanging(object sender, CancelEventArgs<string> e) {
      if (symbols.ContainsKey(e.Value)) e.Cancel = true;
    }
    private void Symbol_NameChanged(object sender, EventArgs e) {
      ISymbol symbol = (ISymbol)sender;
      string oldName = symbols.Where(x => x.Value == symbol).First().Key;
      string newName = symbol.Name;

      symbols.Remove(oldName);
      symbols.Add(newName, symbol);

      var subtreeCount = symbolSubtreeCount[oldName];
      symbolSubtreeCount.Remove(oldName);
      symbolSubtreeCount.Add(newName, subtreeCount);

      List<string> allowedChilds;
      if (allowedChildSymbols.TryGetValue(oldName, out allowedChilds)) {
        allowedChildSymbols.Remove(oldName);
        allowedChildSymbols.Add(newName, allowedChilds);
      }

      for (int i = 0; i < GetMaximumSubtreeCount(symbol); i++) {
        if (allowedChildSymbolsPerIndex.TryGetValue(Tuple.Create(oldName, i), out allowedChilds)) {
          allowedChildSymbolsPerIndex.Remove(Tuple.Create(oldName, i));
          allowedChildSymbolsPerIndex.Add(Tuple.Create(newName, i), allowedChilds);
        }
      }

      foreach (var parent in Symbols) {
        if (allowedChildSymbols.TryGetValue(parent.Name, out allowedChilds))
          if (allowedChilds.Remove(oldName))
            allowedChilds.Add(newName);

        for (int i = 0; i < GetMaximumSubtreeCount(parent); i++) {
          if (allowedChildSymbolsPerIndex.TryGetValue(Tuple.Create(parent.Name, i), out allowedChilds))
            if (allowedChilds.Remove(oldName)) allowedChilds.Add(newName);
        }
      }

      ClearCaches();
      OnChanged();
    }

    private void Symbol_Changed(object sende, EventArgs e) {
      ClearCaches();
      OnChanged();
    }

    private void GroupSymbol_ItemsAdded(object sender, CollectionItemsChangedEventArgs<ISymbol> e) {
      suppressEvents = true;
      foreach (ISymbol symbol in e.Items)
        if (!ContainsSymbol(symbol))
          AddSymbol(symbol);
      suppressEvents = false;
      OnChanged();
    }
    private void GroupSymbol_ItemsRemoved(object sender, CollectionItemsChangedEventArgs<ISymbol> e) {
      suppressEvents = true;
      foreach (ISymbol symbol in e.Items)
        if (ContainsSymbol(symbol))
          RemoveSymbol(symbol);
      suppressEvents = false;
      OnChanged();
    }
    private void GroupSymbol_CollectionReset(object sender, CollectionItemsChangedEventArgs<ISymbol> e) {
      suppressEvents = true;
      foreach (ISymbol symbol in e.Items)
        if (!ContainsSymbol(symbol))
          AddSymbol(symbol);
      foreach (ISymbol symbol in e.OldItems)
        if (ContainsSymbol(symbol))
          RemoveSymbol(symbol);
      suppressEvents = false;
      OnChanged();
    }

    public event EventHandler Changed;
    protected virtual void OnChanged() {
      if (suppressEvents) return;
      var handler = Changed;
      if (handler != null) Changed(this, EventArgs.Empty);
    }
    #endregion
  }
}