feat: Better implementation of DictionaryExtensions.ToInverse

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
  - New XML conversion framework for performance improvements
 ### Changed
  - XmlUtils is now using the improved XML conversion framework 
+ - Better implementation of DictionaryExtensions.ToInverse
 
 ## [5.0.0] - 2018-09-14
 ### Added

ICD.Common.Utils.Tests/Extensions/DictionaryExtensionsTest.cs

@@ -301,5 +301,29 @@ namespace ICD.Common.Utils.Tests.Extensions
 			Assert.AreEqual(20, ordered[1]);
 			Assert.AreEqual(30, ordered[2]);
 		}
+
+		[Test]
+		public void ToInverseTest()
+		{
+			Dictionary<int, string> forward = new Dictionary<int, string>
+			{
+				{ 1, "testA" },
+				{ 2, "testA" },
+				{ 3, "testB" },
+				{ 4, "testB" }
+			};
+
+			Dictionary<string, List<int>> backwards = new Dictionary<string, List<int>>
+			{
+				{"testA", new List<int> {1, 2}},
+				{"testB", new List<int> {3, 4}}
+			};
+
+			Dictionary<string, List<int>> inverse = forward.ToInverse();
+
+			bool equal = inverse.DictionaryEqual(backwards, (v1, v2) => v1.ScrambledEquals(v2));
+
+			Assert.IsTrue(equal);
+		}
 	}
 }

ICD.Common.Utils/Extensions/DictionaryExtensions.cs

@@ -452,12 +452,26 @@ namespace ICD.Common.Utils.Extensions
 		/// <param name="extends"></param>
 		/// <returns></returns>
 		[PublicAPI]
-		public static Dictionary<TValue, TKey> ToInverse<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> extends)
+		public static Dictionary<TValue, List<TKey>> ToInverse<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> extends)
 		{
 			if (extends == null)
 				throw new ArgumentNullException("extends");
 
-			return extends.ToDictionary(kvp => kvp.Value, kvp => kvp.Key);
+			Dictionary<TValue, List<TKey>> output = new Dictionary<TValue, List<TKey>>();
+
+			foreach (KeyValuePair<TKey, TValue> kvp in extends)
+			{
+				List<TKey> keys;
+				if (!output.TryGetValue(kvp.Value, out keys))
+				{
+					keys = new List<TKey>();
+					output.Add(kvp.Value, keys);
+				}
+
+				keys.Add(kvp.Key);
+			}
+
+			return output;
 		}
 	}
 }