Preserve all matching Excel rows when merging

ExcelMatcher.csproj

@@ -4,6 +4,7 @@
     <OutputType Condition="'$(RuntimeIdentifier)' == 'win-x64'">WinExe</OutputType>
     <OutputType Condition="'$(RuntimeIdentifier)' != 'win-x64'">Exe</OutputType>
     <TargetFramework>net8.0</TargetFramework>
+    <Version>1.0.1</Version>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <IncludeNativeLibrariesForSelfExtract>true</IncludeNativeLibrariesForSelfExtract>

ExcelService.cs

@@ -213,6 +213,7 @@ public sealed class MergeOutput
 {
     public List<string> Columns { get; init; } = new();
     public List<string[]> Rows { get; init; } = new();
+    public int[] SecondaryColumnMap { get; init; } = Array.Empty<int>();
 }
 
 public static class TableMatcher
@@ -296,7 +297,7 @@ public static class TableMatcher
 
     private static bool IsEmptyParts(string[] parts) => parts.All(string.IsNullOrEmpty);
 
-    private static string JoinKey(string[] parts) => string.Join("\u00a6", parts);
+    private static string JoinKey(string[] parts) => string.Concat(parts.Select(part => $"{part.Length}:{part};"));
 
     private static bool PartsContain(string[] a, string[] b)
     {
@@ -360,21 +361,24 @@ public static class TableMatcher
 
     private sealed class Candidate
     {
-        public string[]? BRow;
+        public List<(string[] Row, double Score)> BRows = new();
         public string Type = "";
-        public double Score;
-        public int BCount;
     }
 
     private static List<Candidate> MatchMain(TableData main, TableData secondary, MatchOptions o, out List<string[]> onlySecondary)
     {
         var mainIdx = KeyIndexes(o.MainUsed);
         var secIdx = KeyIndexes(o.SecondaryUsed);
-        int keyCount = Math.Min(mainIdx.Count, secIdx.Count);
+        if (mainIdx.Count != secIdx.Count)
+            throw new ArgumentException("Выберите одинаковое число ключевых колонок в обеих таблицах.");
+        int keyCount = mainIdx.Count;
         onlySecondary = new List<string[]>();
 
         if (keyCount == 0)
-            return main.Rows.Select(_ => (Candidate?)null).Cast<Candidate>().ToList();
+        {
+            onlySecondary.AddRange(secondary.Rows);
+            return main.Rows.Select(_ => new Candidate()).ToList();
+        }
 
         var token = o.Token;
         bool or = o.UseOr;
@@ -388,34 +392,38 @@ public static class TableMatcher
                 foreach (var row in main.Rows)
                 {
                     var parts = RowParts(row, mainIdx, keyCount, o);
-                    if (!IsEmptyParts(parts)) mainKeys.Add(JoinKey(parts));
+                    if (parts.All(part => !string.IsNullOrEmpty(part))) mainKeys.Add(JoinKey(parts));
                 }
 
-                var bByKey = new Dictionary<string, (string[] Row, int Count)>(StringComparer.Ordinal);
+                var bByKey = new Dictionary<string, List<string[]>>(StringComparer.Ordinal);
                 foreach (var row in secondary.Rows)
                 {
                     token.ThrowIfCancellationRequested();
                     var parts = RowParts(row, secIdx, keyCount, o);
-                    if (IsEmptyParts(parts)) continue;
+                    if (parts.Any(string.IsNullOrEmpty)) continue;
                     var k = JoinKey(parts);
-                    if (bByKey.TryGetValue(k, out var cur))
-                        bByKey[k] = (cur.Row, cur.Count + 1);
+                    if (bByKey.TryGetValue(k, out var rows))
+                        rows.Add(row);
                     else
-                        bByKey[k] = (row, 1);
+                        bByKey[k] = new List<string[]> { row };
                 }
 
                 foreach (var row in main.Rows)
                 {
                     token.ThrowIfCancellationRequested();
                     var parts = RowParts(row, mainIdx, keyCount, o);
-                    if (IsEmptyParts(parts))
+                    if (parts.Any(string.IsNullOrEmpty))
                     {
                         candidates.Add(new Candidate());
                         continue;
                     }
                     if (bByKey.TryGetValue(JoinKey(parts), out var hit))
                     {
-                        candidates.Add(new Candidate { BRow = hit.Row, Type = "точное", Score = 100, BCount = hit.Count });
+                        candidates.Add(new Candidate
+                        {
+                            Type = "точное",
+                            BRows = hit.Select(row => (row, 100.0)).ToList()
+                        });
                     }
                     else
                     {
@@ -427,7 +435,7 @@ public static class TableMatcher
                 {
                     token.ThrowIfCancellationRequested();
                     var parts = RowParts(row, secIdx, keyCount, o);
-                    if (!IsEmptyParts(parts) && !mainKeys.Contains(JoinKey(parts)))
+                    if (parts.Any(string.IsNullOrEmpty) || !mainKeys.Contains(JoinKey(parts)))
                         onlySecondary.Add(row);
                 }
             }
@@ -443,21 +451,21 @@ public static class TableMatcher
                         if (parts[j].Length > 0) mainSets[j].Add(parts[j]);
                 }
 
-                var bByVal = new Dictionary<string, (string[] Row, int Count)>[keyCount];
-                for (int j = 0; j < keyCount; j++) bByVal[j] = new Dictionary<string, (string[] Row, int Count)>(StringComparer.Ordinal);
-                foreach (var row in secondary.Rows)
+                var bByVal = new Dictionary<string, List<int>>[keyCount];
+                for (int j = 0; j < keyCount; j++) bByVal[j] = new Dictionary<string, List<int>>(StringComparer.Ordinal);
+                for (int rowIndex = 0; rowIndex < secondary.Rows.Count; rowIndex++)
                 {
                     token.ThrowIfCancellationRequested();
-                    var parts = RowParts(row, secIdx, keyCount, o);
+                    var parts = RowParts(secondary.Rows[rowIndex], secIdx, keyCount, o);
                     if (IsEmptyParts(parts)) continue;
                     for (int j = 0; j < keyCount; j++)
                     {
                         if (parts[j].Length == 0) continue;
                         var v = parts[j];
-                        if (bByVal[j].TryGetValue(v, out var cur))
-                            bByVal[j][v] = (cur.Row, cur.Count + 1);
+                        if (bByVal[j].TryGetValue(v, out var rowIndexes))
+                            rowIndexes.Add(rowIndex);
                         else
-                            bByVal[j][v] = (row, 1);
+                            bByVal[j][v] = new List<int> { rowIndex };
                     }
                 }
 
@@ -470,28 +478,28 @@ public static class TableMatcher
                         candidates.Add(new Candidate());
                         continue;
                     }
-                    string[]? bestRow = null;
-                    int bestCount = 0;
+                    var matchedRows = new HashSet<int>();
                     for (int j = 0; j < keyCount; j++)
                     {
                         if (parts[j].Length == 0) continue;
-                        if (bByVal[j].TryGetValue(parts[j], out var hit) && hit.Count > bestCount)
-                        {
-                            bestRow = hit.Row;
-                            bestCount = hit.Count;
-                        }
+                        if (bByVal[j].TryGetValue(parts[j], out var rowIndexes))
+                            foreach (var rowIndex in rowIndexes) matchedRows.Add(rowIndex);
                     }
-                    if (bestRow is not null)
-                        candidates.Add(new Candidate { BRow = bestRow, Type = "точное", Score = 100, BCount = bestCount });
-                    else
-                        candidates.Add(new Candidate());
+                    var candidate = new Candidate { Type = "точное" };
+                    foreach (var rowIndex in matchedRows.OrderBy(index => index))
+                        candidate.BRows.Add((secondary.Rows[rowIndex], 100.0));
+                    candidates.Add(candidate);
                 }
 
                 foreach (var row in secondary.Rows)
                 {
                     token.ThrowIfCancellationRequested();
                     var parts = RowParts(row, secIdx, keyCount, o);
-                    if (IsEmptyParts(parts)) continue;
+                    if (IsEmptyParts(parts))
+                    {
+                        onlySecondary.Add(row);
+                        continue;
+                    }
                     bool matched = false;
                     for (int j = 0; j < keyCount; j++)
                     {
@@ -518,15 +526,13 @@ public static class TableMatcher
         {
             token.ThrowIfCancellationRequested();
             var parts = RowParts(row, mainIdx, keyCount, o);
-            if (IsEmptyParts(parts))
+            if (IsEmptyParts(parts) || (!or && parts.Any(string.IsNullOrEmpty)))
             {
                 candidates.Add(new Candidate());
                 continue;
             }
 
-            string[]? bestRow = null;
-            double bestScore = 0;
-            int hitCount = 0;
+            var candidate = new Candidate { Type = o.Kind == MatchKind.Partial ? "частичное" : "нечёткое" };
 
             if (o.Kind == MatchKind.Partial)
             {
@@ -536,13 +542,9 @@ public static class TableMatcher
                     bool ok = or ? AnyColContains(parts, b.Parts) : PartsContain(parts, b.Parts);
                     if (!ok) continue;
                     hits[i] = true;
-                    hitCount++;
-                    if (bestRow is null) bestRow = b.Row;
+                    candidate.BRows.Add((b.Row, 100.0));
                 }
-                if (bestRow is not null)
-                    candidates.Add(new Candidate { BRow = bestRow, BCount = hitCount, Score = 100, Type = "частичное" });
-                else
-                    candidates.Add(new Candidate());
+                candidates.Add(candidate);
             }
             else
             {
@@ -550,28 +552,15 @@ public static class TableMatcher
                 for (int i = 0; i < secRows.Count; i++)
                 {
                     var b = secRows[i];
+                    if (!or && b.Parts.Any(string.IsNullOrEmpty)) continue;
                     double sim = ColumnSim(parts, b.Parts, or);
                     if (sim >= threshold)
                     {
                         hits[i] = true;
-                        hitCount++;
-                        if (sim > bestScore)
-                        {
-                            bestScore = sim;
-                            bestRow = b.Row;
-                        }
+                        candidate.BRows.Add((b.Row, Math.Round(sim * 100, 1)));
                     }
                 }
-                if (bestRow is not null)
-                    candidates.Add(new Candidate
-                    {
-                        BRow = bestRow,
-                        BCount = hitCount,
-                        Score = Math.Round(bestScore * 100, 1),
-                        Type = "нечёткое"
-                    });
-                else
-                    candidates.Add(new Candidate());
+                candidates.Add(candidate);
             }
         }
 
@@ -596,20 +585,23 @@ public static class TableMatcher
         {
             o.Token.ThrowIfCancellationRequested();
             var c = candidates[i];
-            if (c.BRow is null)
+            if (c.BRows.Count == 0)
             {
                 onlyMain.Add(main.Rows[i]);
                 continue;
             }
             matches.Add(main.Rows[i]);
-            pairs.Add(new MatchPair
+            foreach (var matched in c.BRows)
             {
-                RowA = main.Rows[i],
-                RowB = c.BRow,
-                Type = c.Type,
-                Score = c.Score,
-                BCount = c.BCount
-            });
+                pairs.Add(new MatchPair
+                {
+                    RowA = main.Rows[i],
+                    RowB = matched.Row,
+                    Type = c.Type,
+                    Score = matched.Score,
+                    BCount = c.BRows.Count
+                });
+            }
         }
 
         return new MatchResult
@@ -633,65 +625,98 @@ public static class TableMatcher
             Kind = partial ? MatchKind.Partial : MatchKind.Exact
         });
 
-    public static MergeOutput Merge(TableData main, TableData secondary, MatchOptions o, bool removeIdenticalColumns = true)
+    public static MergeOutput Merge(TableData main, TableData secondary, MatchOptions o, bool mergeColumnsByHeader = true)
     {
         var candidates = MatchMain(main, secondary, o, out _);
-
         var columns = new List<string>(main.Columns);
-        var extraCols = new List<int>();
+        var secondaryColumnMap = new int[secondary.Columns.Count];
+        var commonMainColumn = Enumerable.Repeat(-1, secondary.Columns.Count).ToArray();
+        var usedMainColumns = new HashSet<int>();
+        var conflictingSecondaryColumns = new bool[secondary.Columns.Count];
 
-        if (removeIdenticalColumns)
+        if (mergeColumnsByHeader)
         {
             for (int j = 0; j < secondary.Columns.Count; j++)
             {
-                if (columns.Contains(secondary.Columns[j]))
-                    continue;
-
-                var target = SortedColumnValues(secondary.Rows, j);
-                bool duplicate = false;
-                for (int c = 0; c < main.Columns.Count && !duplicate; c++)
-                    duplicate = ColumnValuesEqual(target, SortedColumnValues(main.Rows, c));
-                for (int e = 0; e < extraCols.Count && !duplicate; e++)
-                    duplicate = ColumnValuesEqual(target, SortedColumnValues(secondary.Rows, extraCols[e]));
-                if (duplicate) continue;
-
-                columns.Add(secondary.Columns[j]);
-                extraCols.Add(j);
-            }
-        }
-        else
-        {
-            for (int j = 0; j < secondary.Columns.Count; j++)
-            {
-                columns.Add(secondary.Columns[j]);
-                extraCols.Add(j);
+                commonMainColumn[j] = Enumerable.Range(0, main.Columns.Count)
+                    .FirstOrDefault(c => !usedMainColumns.Contains(c) &&
+                        string.Equals(main.Columns[c].Trim(), secondary.Columns[j].Trim(), StringComparison.OrdinalIgnoreCase), -1);
+                if (commonMainColumn[j] >= 0) usedMainColumns.Add(commonMainColumn[j]);
             }
         }
 
-        string[] BuildMerged(string[] row, string[] secRow)
+        // If same-named fields contain different non-empty values in any matched
+        // pair, keep the B value in its own column instead of silently discarding it.
+        for (int i = 0; i < candidates.Count && i < main.RowCount; i++)
         {
-            var merged = new string[columns.Count];
-            for (int c = 0; c < main.Columns.Count; c++)
-                merged[c] = c < row.Length ? row[c] : "";
-            for (int e = 0; e < extraCols.Count; e++)
+            foreach (var match in candidates[i].BRows)
             {
-                int j = extraCols[e];
-                merged[main.Columns.Count + e] = j < secRow.Length ? secRow[j] : "";
+                for (int j = 0; j < secondary.Columns.Count; j++)
+                {
+                    int a = commonMainColumn[j];
+                    if (a < 0) continue;
+                    string av = a < main.Rows[i].Length ? main.Rows[i][a] : "";
+                    string bv = j < match.Row.Length ? match.Row[j] : "";
+                    if (!string.IsNullOrWhiteSpace(av) && !string.IsNullOrWhiteSpace(bv) &&
+                        !string.Equals(av, bv, StringComparison.Ordinal))
+                        conflictingSecondaryColumns[j] = true;
+                }
             }
-            return merged;
+        }
+
+        int AddUniqueColumn(string header)
+        {
+            string baseHeader = string.IsNullOrWhiteSpace(header) ? "Колонка B" : header;
+            string unique = baseHeader;
+            int suffix = 2;
+            while (columns.Contains(unique, StringComparer.OrdinalIgnoreCase))
+                unique = $"{baseHeader} ({suffix++})";
+            columns.Add(unique);
+            return columns.Count - 1;
+        }
+
+        for (int j = 0; j < secondary.Columns.Count; j++)
+        {
+            if (mergeColumnsByHeader && commonMainColumn[j] >= 0 && !conflictingSecondaryColumns[j])
+            {
+                secondaryColumnMap[j] = commonMainColumn[j];
+                continue;
+            }
+
+            string header = secondary.Columns[j];
+            if (!mergeColumnsByHeader || commonMainColumn[j] >= 0 || columns.Contains(header, StringComparer.OrdinalIgnoreCase))
+                header = "B: " + header;
+            secondaryColumnMap[j] = AddUniqueColumn(header);
         }
 
         var rows = new List<string[]>();
-        int n = Math.Min(candidates.Count, main.RowCount);
-        for (int i = 0; i < n; i++)
+        for (int i = 0; i < candidates.Count && i < main.RowCount; i++)
         {
             o.Token.ThrowIfCancellationRequested();
-            var c = candidates[i];
-            if (c.BRow is not null)
-                rows.Add(BuildMerged(main.Rows[i], c.BRow));
+            foreach (var match in candidates[i].BRows)
+            {
+                var merged = new string[columns.Count];
+                Array.Fill(merged, "");
+                for (int c = 0; c < main.Columns.Count; c++)
+                    if (c < main.Rows[i].Length) merged[c] = main.Rows[i][c];
+                for (int j = 0; j < secondaryColumnMap.Length; j++)
+                {
+                    string bv = j < match.Row.Length ? match.Row[j] : "";
+                    int destination = secondaryColumnMap[j];
+                    if (commonMainColumn[j] >= 0 && !conflictingSecondaryColumns[j])
+                    {
+                        if (string.IsNullOrWhiteSpace(merged[destination])) merged[destination] = bv;
+                    }
+                    else
+                    {
+                        merged[destination] = bv;
+                    }
+                }
+                rows.Add(merged);
+            }
         }
 
-        return new MergeOutput { Columns = columns, Rows = rows };
+        return new MergeOutput { Columns = columns, Rows = rows, SecondaryColumnMap = secondaryColumnMap };
     }
 
     public static MergeOutput Merge(
@@ -701,51 +726,26 @@ public static class TableMatcher
         bool[] secondaryUsed,
         bool ignoreCaseAndSpaces,
         bool partial = false,
-        bool removeIdenticalColumns = true)
+        bool mergeColumnsByHeader = true)
         => Merge(main, secondary, new MatchOptions
         {
             MainUsed = mainUsed,
             SecondaryUsed = secondaryUsed,
             IgnoreCaseAndSpaces = ignoreCaseAndSpaces,
             Kind = partial ? MatchKind.Partial : MatchKind.Exact
-        }, removeIdenticalColumns);
-
-    private static List<string> SortedColumnValues(List<string[]> rows, int colIndex)
-    {
-        var vals = new List<string>();
-        foreach (var r in rows)
-            vals.Add(colIndex < r.Length ? (r[colIndex] ?? "").Trim() : "");
-        vals.Sort(StringComparer.Ordinal);
-        return vals;
-    }
-
-    private static bool ColumnValuesEqual(List<string> a, List<string> b)
-    {
-        if (a.Count != b.Count) return false;
-        for (int i = 0; i < a.Count; i++)
-            if (!string.Equals(a[i], b[i], StringComparison.Ordinal)) return false;
-        return true;
-    }
+        }, mergeColumnsByHeader);
 
     public static (TableData Table, int Removed) Dedupe(TableData table, bool[] used, bool ignore, MatchOptions? template = null)
     {
-        var idx = KeyIndexes(used);
-        if (idx.Count == 0)
-            return (table, 0);
-
         var o = template?.Clone() ?? new MatchOptions();
-        o.MainUsed = used;
-        o.SecondaryUsed = used;
-        o.IgnoreCaseAndSpaces = ignore;
-
         var seen = new HashSet<string>(StringComparer.Ordinal);
         var rows = new List<string[]>();
         int removed = 0;
         foreach (var row in table.Rows)
         {
             o.Token.ThrowIfCancellationRequested();
-            var parts = RowParts(row, idx, idx.Count, o);
-            if (!IsEmptyParts(parts) && !seen.Add(JoinKey(parts)))
+            var parts = row.Select(value => value ?? "").ToArray();
+            if (!seen.Add(JoinKey(parts)))
             {
                 removed++;
                 continue;
@@ -849,9 +849,10 @@ public static class ExcelExporter
             }
             if (withMeta)
             {
-                var type = result.Pairs.Count > i ? result.Pairs[i].Type : "";
-                var score = result.Pairs.Count > i ? result.Pairs[i].Score : 0;
-                var count = result.Pairs.Count > i ? result.Pairs[i].BCount : 0;
+                var rowPairs = result.Pairs.Where(p => ReferenceEquals(p.RowA, row)).ToList();
+                var type = rowPairs.FirstOrDefault()?.Type ?? "";
+                var score = rowPairs.Count == 0 ? 0 : rowPairs.Max(p => p.Score);
+                var count = rowPairs.Count;
                 SetCell(ws, i + 2, baseCols + 1, type);
                 SetCell(ws, i + 2, baseCols + 2, type == "нечёткое" ? score.ToString("0.#", CultureInfo.InvariantCulture) : "");
                 SetCell(ws, i + 2, baseCols + 3, count == 0 ? "" : count.ToString(CultureInfo.InvariantCulture));
@@ -927,8 +928,9 @@ public static class ExcelExporter
         Row("Из них частичных", partial);
         Row("Из них нечётких", fuzzy);
 
-        double avg = result.Pairs.Count == 0 ? 0 : Math.Round(result.Pairs.Average(p => p.BCount), 2);
-        int maxBC = result.Pairs.Count == 0 ? 0 : result.Pairs.Max(p => p.BCount);
+        var countsPerMainRow = result.Pairs.GroupBy(p => p.RowA).Select(group => group.First().BCount).ToList();
+        double avg = countsPerMainRow.Count == 0 ? 0 : Math.Round(countsPerMainRow.Average(), 2);
+        int maxBC = countsPerMainRow.Count == 0 ? 0 : countsPerMainRow.Max();
         Row("Среднее B-совпадений (N→M)", avg);
         Row("Максимум B-совпадений (N→M)", maxBC);
 

MainWindow.cs

@@ -137,8 +137,8 @@ public sealed class MainWindow : Window
     private readonly RadioButton _rbBoth = new() { Content = "Совпадения + чего нет в A" };
     private readonly RadioButton _rbExact = new() { Content = "Точное совпадение", IsChecked = true };
     private readonly RadioButton _rbPartial = new() { Content = "Частичное (по фрагменту)" };
-    private readonly CheckBox _chkDedupe = new() { Content = "Удалять дубликаты по ключевым колонкам" };
-    private readonly CheckBox _chkCleanCols = new() { Content = "Убирать одинаковые колонки после слияния", IsChecked = true };
+    private readonly CheckBox _chkDedupe = new() { Content = "Удалять полностью одинаковые строки" };
+    private readonly CheckBox _chkCleanCols = new() { Content = "Объединять одноимённые колонки", IsChecked = true };
 
     private readonly RadioButton _rbFuzzy = new() { Content = "Нечёткое (по сходству %)" };
     private readonly Slider _slFuzzy = new()
@@ -561,7 +561,7 @@ private Control BuildFilePanel(TextBox tb, Button browse, ComboBox cb, StackPane
 
         var colLabel = new TextBlock
         {
-            Text = "Ключевые колонки для сопоставления",
+            Text = "Ключи (выберите соответствующие поля в одинаковом порядке)",
             Foreground = Ui.Muted,
             FontWeight = FontWeight.SemiBold,
             FontSize = 12
@@ -900,6 +900,11 @@ private Control BuildFilePanel(TextBox tb, Button browse, ComboBox cb, StackPane
             ShowError("Отметьте хотя бы одну ключевую колонку в каждой таблице (по умолчанию отмечена первая).");
             return;
         }
+        if (mainUsed.Count(x => x) != secUsed.Count(x => x))
+        {
+            ShowError("Выберите одинаковое число ключевых колонок в обеих таблицах.");
+            return;
+        }
 
         var cts = new CancellationTokenSource();
         _cts = cts;
@@ -978,8 +983,9 @@ private Control BuildFilePanel(TextBox tb, Button browse, ComboBox cb, StackPane
         sb.Append($"Совпадений: {r.Matches.Count} · Только в A: {r.OnlyMain.Count} · Только в B: {r.OnlySecondary.Count}.");
         if (r.Pairs.Count > 0)
         {
-            double avg = Math.Round(r.Pairs.Average(p => p.BCount), 2);
-            int max = r.Pairs.Max(p => p.BCount);
+            var countsPerMainRow = r.Pairs.GroupBy(p => p.RowA).Select(group => group.First().BCount).ToList();
+            double avg = Math.Round(countsPerMainRow.Average(), 2);
+            int max = countsPerMainRow.Max();
             sb.Append($" Пары A↔B: {r.Pairs.Count}, ср. N→M: {avg.ToString(CultureInfo.InvariantCulture)}, макс: {max}.");
         }
         sb.Append($" Ключи заполнены: A={covA.ToString(CultureInfo.InvariantCulture)}%, B={covB.ToString(CultureInfo.InvariantCulture)}%.");
@@ -1081,59 +1087,27 @@ private Control BuildFilePanel(TextBox tb, Button browse, ComboBox cb, StackPane
                 break;
 
             default:
-                // Build a union of both schemas. Columns with the same header are
-                // aligned; B-only columns get their own position in the result.
-                headers = new List<string>(main.Columns);
-                var mainColumnMap = Enumerable.Range(0, main.Columns.Count).ToArray();
-                var secondaryColumnMap = new int[sec.Columns.Count];
-                var matchedSecondaryColumns = new HashSet<int>();
-
-                for (int b = 0; b < sec.Columns.Count; b++)
-                {
-                    int matchingMain = -1;
-                    for (int a = 0; a < main.Columns.Count; a++)
-                    {
-                        if (!matchedSecondaryColumns.Contains(a) &&
-                            string.Equals(main.Columns[a].Trim(), sec.Columns[b].Trim(), StringComparison.OrdinalIgnoreCase))
-                        {
-                            matchingMain = a;
-                            break;
-                        }
-                    }
-
-                    if (matchingMain >= 0)
-                    {
-                        secondaryColumnMap[b] = matchingMain;
-                        matchedSecondaryColumns.Add(matchingMain);
-                    }
-                    else
-                    {
-                        var header = sec.Columns[b];
-                        if (headers.Contains(header, StringComparer.OrdinalIgnoreCase))
-                            header = $"B: {header}";
-                        secondaryColumnMap[b] = headers.Count;
-                        headers.Add(header);
-                    }
-                }
-
-                string[] CombineRows(string[] rowA, string[] rowB)
-                {
-                    var combined = new string[headers.Count];
-                    Array.Fill(combined, "");
-                    for (int a = 0; a < mainColumnMap.Length && a < rowA.Length; a++)
-                        combined[mainColumnMap[a]] = rowA[a];
-                    for (int b = 0; b < secondaryColumnMap.Length && b < rowB.Length; b++)
-                        combined[secondaryColumnMap[b]] = rowB[b];
-                    return combined;
-                }
-
-                foreach (var pair in result.Pairs)
-                    data.Add(CombineRows(pair.RowA, pair.RowB));
+                headers = _merged?.Columns ?? new List<string>(main.Columns);
+                data = _merged is not null ? new List<string[]>(_merged.Rows) : new List<string[]>();
                 sources = new List<string>();
                 foreach (var _ in result.Pairs) sources.Add("A+B");
                 foreach (var r in result.OnlySecondary)
                 {
-                    data.Add(CombineRows(Array.Empty<string>(), r));
+                    var row = new string[headers.Count];
+                    Array.Fill(row, "");
+                    if (_merged is not null)
+                    {
+                        for (int b = 0; b < _merged.SecondaryColumnMap.Length && b < r.Length; b++)
+                        {
+                            int destination = _merged.SecondaryColumnMap[b];
+                            if (destination >= 0 && destination < row.Length) row[destination] = r[b];
+                        }
+                    }
+                    else
+                    {
+                        for (int b = 0; b < r.Length && b < row.Length; b++) row[b] = r[b];
+                    }
+                    data.Add(row);
                     sources.Add("B");
                 }
                 break;