1 files changed, 108 insertions, 0 deletions
diff --git a/Rx/NET/Source/System.Reactive.Linq/Reactive/Linq/Observable/MinBy.cs b/Rx/NET/Source/System.Reactive.Linq/Reactive/Linq/Observable/MinBy.cs
new file mode 100644
index 0000000..a32bf92
--- /dev/null
+++ b/Rx/NET/Source/System.Reactive.Linq/Reactive/Linq/Observable/MinBy.cs
@@ -0,0 +1,108 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
+
+#if !NO_PERF
+using System;
+using System.Collections.Generic;
+
+namespace System.Reactive.Linq.Observαble
+{
+    class MinBy<TSource, TKey> : Producer<IList<TSource>>
+    {
+        private readonly IObservable<TSource> _source;
+        private readonly Func<TSource, TKey> _keySelector;
+        private readonly IComparer<TKey> _comparer;
+
+        public MinBy(IObservable<TSource> source, Func<TSource, TKey> keySelector, IComparer<TKey> comparer)
+        {
+            _source = source;
+            _keySelector = keySelector;
+            _comparer = comparer;
+        }
+
+        protected override IDisposable Run(IObserver<IList<TSource>> observer, IDisposable cancel, Action<IDisposable> setSink)
+        {
+            var sink = new _(this, observer, cancel);
+            setSink(sink);
+            return _source.SubscribeSafe(sink);
+        }
+
+        class _ : Sink<IList<TSource>>, IObserver<TSource>
+        {
+            private readonly MinBy<TSource, TKey> _parent;
+            private bool _hasValue;
+            private TKey _lastKey;
+            private List<TSource> _list;
+
+            public _(MinBy<TSource, TKey> parent, IObserver<IList<TSource>> observer, IDisposable cancel)
+                : base(observer, cancel)
+            {
+                _parent = parent;
+
+                _hasValue = false;
+                _lastKey = default(TKey);
+                _list = new List<TSource>();
+            }
+
+            public void OnNext(TSource value)
+            {
+                var key = default(TKey);
+                try
+                {
+                    key = _parent._keySelector(value);
+                }
+                catch (Exception ex)
+                {
+                    base._observer.OnError(ex);
+                    base.Dispose();
+                    return;
+                }
+
+                var comparison = 0;
+
+                if (!_hasValue)
+                {
+                    _hasValue = true;
+                    _lastKey = key;
+                }
+                else
+                {
+                    try
+                    {
+                        comparison = _parent._comparer.Compare(key, _lastKey);
+                    }
+                    catch (Exception ex)
+                    {
+                        base._observer.OnError(ex);
+                        base.Dispose();
+                        return;
+                    }
+                }
+
+                if (comparison < 0)
+                {
+                    _lastKey = key;
+                    _list.Clear();
+                }
+
+                if (comparison <= 0)
+                {
+                    _list.Add(value);
+                }
+            }
+
+            public void OnError(Exception error)
+            {
+                base._observer.OnError(error);
+                base.Dispose();
+            }
+
+            public void OnCompleted()
+            {
+                base._observer.OnNext(_list);
+                base._observer.OnCompleted();
+                base.Dispose();
+            }
+        }
+    }
+}
+#endif
+\ No newline at end of file