Merge pull request #122 from El-Gor-do/fix-issue-121

Equalise the length of non-numeric tokens before sorting

Author: tompazourek

src/NaturalSort.Extension/NaturalSortComparer.cs

@@ -152,27 +152,36 @@ public int Compare(string str1, string str2)
                 if (paddingCompare != 0)
                     return paddingCompare;
             }
-            else if (_stringComparer is not null)
-            {
-                // compare both tokens as strings
-                var tokenString1 = str1.Substring(startIndex1, rangeLength1);
-                var tokenString2 = str2.Substring(startIndex2, rangeLength2);
-                var stringCompare = _stringComparer.Compare(tokenString1, tokenString2);
-                if (stringCompare != 0)
-                    return stringCompare;
-            }
             else
             {
-                // use string comparison
-                var minLength = Math.Min(rangeLength1, rangeLength2);
-                var stringCompare = string.Compare(str1, startIndex1, str2, startIndex2, minLength, _stringComparison);
-                if (stringCompare == 0)
+                // only compare non-numeric tokens up to the shorter of their lengths
+                if (rangeLength1 < rangeLength2)
                 {
-                    stringCompare = rangeLength1 - rangeLength2;
+                    rangeLength2 = rangeLength1;
+                    endIndex2 = startIndex2 + rangeLength2;
+                }
+                else if (rangeLength2 < rangeLength1)
+                {
+                    rangeLength1 = rangeLength2;
+                    endIndex1 = startIndex1 + rangeLength1;
                 }
 
-                if (stringCompare != 0)
-                    return stringCompare;
+                if (_stringComparer is not null)
+                {
+                    // compare both tokens as strings
+                    var tokenString1 = str1.Substring(startIndex1, rangeLength1);
+                    var tokenString2 = str2.Substring(startIndex2, rangeLength2);
+                    var stringCompare = _stringComparer.Compare(tokenString1, tokenString2);
+                    if (stringCompare != 0)
+                        return stringCompare;
+                }
+                else
+                {
+                    // use string comparison
+                    var stringCompare = string.Compare(str1, startIndex1, str2, startIndex2, rangeLength1, _stringComparison);
+                    if (stringCompare != 0)
+                        return stringCompare;
+                }
             }
 
             startIndex1 = endIndex1;

tests/NaturalSort.Extension.Tests/NaturalSortComparerTests.cs

@@ -65,6 +65,14 @@ private static void RunTests_StringComparisonOrdinalIgnoreCase(string[] input, s
         new[] { "A", "A10", "A11", "Z", "A੨", "A੨੨" },
         new[] { "A", "A੨", "A10", "A11", "A੨੨", "Z" }
     )]
+    [InlineData(
+        new[] { "a_abc", "a__abc" },
+        new[] { "a__abc", "a_abc" }
+    )]
+    [InlineData(
+        new[] { "a_abc", "a__abc", "a_123", "a__123", "a_9" },
+        new[] { "a__123", "a__abc", "a_9", "a_123", "a_abc" }
+    )]
     public void WindowsExplorer(string[] input, string[] expected) => RunTests(input, expected);
 
     /// <remarks>