source: branches/FitnessLandscapeAnalysis/HeuristicLab.Analysis.FitnessLandscape/Analysis/EnumerableExtensions.cs @ 11598

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2010 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;
namespace HeuristicLab.Analysis.FitnessLandscape {

  public static class Utils {

    public static IEnumerable<TResult> Delta<T, TResult>(this IEnumerable<T> values, Func<T, T, TResult> f) {
      var it = values.GetEnumerator();
      T last = default(T);
      if (it.MoveNext())
        last = it.Current;
      while (it.MoveNext()) {
        yield return f(last, it.Current);
        last = it.Current;
      }
    }

    public static IEnumerable<IEnumerable<TSource>> GroupConsecutive<TSource, TKey>(
        this IEnumerable<TSource> source, Func<TSource, TKey> keySelector) {
      if (source == null) throw new ArgumentNullException("source");
      if (keySelector == null) throw new ArgumentNullException("keySelector");

      var comparer = EqualityComparer<TKey>.Default;
      var grouped = new List<TSource>();
      using (var iter = source.GetEnumerator()) {
        if (!iter.MoveNext()) yield break;
        grouped.Add(iter.Current);
        var last = iter.Current;
        while (iter.MoveNext()) {
          if (!comparer.Equals(keySelector(iter.Current), keySelector(last))) {
            yield return grouped.AsReadOnly();
            grouped = new List<TSource>();
          }
          grouped.Add(iter.Current);
          last = iter.Current;
        }
        yield return grouped.AsReadOnly();
      }
    }
  }
}