table: support vertical merge in HTML rendering

table/config.go

@@ -25,8 +25,8 @@ type ColumnConfig struct {
 	// AutoMerge merges cells with similar values and prevents separators from
 	// being drawn. Caveats:
 	// * VAlign is applied on the individual cell and not on the merged cell
-	// * Does not work in CSV/HTML/Markdown render modes
 	// * Does not work well with horizontal auto-merge (RowConfig.AutoMerge)
+	// * Does not work in CSV/Markdown render modes
 	//
 	// Works best when:
 	// * Style().Options.SeparateRows == true

table/render.go

@@ -67,7 +67,7 @@ func (t *Table) renderColumn(out *strings.Builder, row rowStr, colIdx int, maxCo
 	}
 
 	// extract the text, convert-case if not-empty and align horizontally
-	mergeVertically := t.shouldMergeCellsVertically(colIdx, hint)
+	mergeVertically := t.shouldMergeCellsVerticallyAbove(colIdx, hint)
 	var colStr string
 	if mergeVertically {
 		// leave colStr empty; align will expand the column as necessary

table/render_html.go

@@ -159,6 +159,10 @@ func (t *Table) htmlRenderRow(out *strings.Builder, row rowStr, hint renderHint)
 		if colIdx == 0 && t.autoIndex {
 			t.htmlRenderColumnAutoIndex(out, hint)
 		}
+		// auto-merged columns should be skipped
+		if t.shouldMergeCellsVerticallyAbove(colIdx, hint) {
+			continue
+		}
 
 		align := t.getAlign(colIdx, hint)
 		rowConfig := t.getRowConfig(hint)
@@ -184,6 +188,9 @@ func (t *Table) htmlRenderRow(out *strings.Builder, row rowStr, hint renderHint)
 		if extraColumnsRendered > 0 {
 			out.WriteString(" colspan=")
 			out.WriteString(fmt.Sprint(extraColumnsRendered + 1))
+		} else if rowSpan := t.shouldMergeCellsVerticallyBelow(colIdx, hint); rowSpan > 1 {
+			out.WriteString(" rowspan=")
+			out.WriteString(fmt.Sprint(rowSpan))
 		}
 		out.WriteString(">")
 		if len(colStr) == 0 {
@@ -222,6 +229,7 @@ func (t *Table) htmlRenderRows(out *strings.Builder, rows []rowStr, hint renderH
 				t.htmlRenderRow(out, row, hint)
 				shouldRenderTagClose = true
 			}
+			t.firstRowOfPage = false
 		}
 		if shouldRenderTagClose {
 			out.WriteString("  </")

table/render_html_test.go

@@ -518,6 +518,44 @@ func TestTable_RenderHTML_Sorted(t *testing.T) {
 </table>`)
 }
 
+func TestTable_RenderHTML_ColAutoMerge(t *testing.T) {
+	t.Run("simple", func(t *testing.T) {
+		tw := NewWriter()
+		tw.AppendHeader(Row{"A", "B", "C"})
+		tw.AppendRow(Row{"Y", "Y", 1})
+		tw.AppendRow(Row{"Y", "N", 2})
+		tw.AppendRow(Row{"Y", "N", 3})
+		tw.SetColumnConfigs([]ColumnConfig{
+			{Name: "A", AutoMerge: true},
+			{Name: "B", AutoMerge: true},
+		})
+		compareOutput(t, tw.RenderHTML(), `
+<table class="go-pretty-table">
+  <thead>
+  <tr>
+    <th>A</th>
+    <th>B</th>
+    <th align="right">C</th>
+  </tr>
+  </thead>
+  <tbody>
+  <tr>
+    <td rowspan=3>Y</td>
+    <td>Y</td>
+    <td align="right">1</td>
+  </tr>
+  <tr>
+    <td rowspan=2>N</td>
+    <td align="right">2</td>
+  </tr>
+  <tr>
+    <td align="right">3</td>
+  </tr>
+  </tbody>
+</table>`)
+	})
+}
+
 func TestTable_RenderHTML_RowAutoMerge(t *testing.T) {
 	t.Run("simple", func(t *testing.T) {
 		rcAutoMerge := RowConfig{AutoMerge: true}
@@ -544,6 +582,7 @@ func TestTable_RenderHTML_RowAutoMerge(t *testing.T) {
   </tbody>
 </table>`)
 	})
+
 	t.Run("merged and unmerged entries", func(t *testing.T) {
 		rcAutoMerge := RowConfig{AutoMerge: true}
 		tw := NewWriter()

table/table.go

@@ -431,7 +431,7 @@ func (t *Table) getBorderLeft(hint renderHint) string {
 	} else if hint.isSeparatorRow {
 		if t.autoIndex && hint.isHeaderOrFooterSeparator() {
 			border = t.style.Box.Left
-		} else if !t.autoIndex && t.shouldMergeCellsVertically(0, hint) {
+		} else if !t.autoIndex && t.shouldMergeCellsVerticallyAbove(0, hint) {
 			border = t.style.Box.Left
 		} else {
 			border = t.style.Box.LeftSeparator
@@ -451,7 +451,7 @@ func (t *Table) getBorderRight(hint renderHint) string {
 	} else if hint.isBorderBottom {
 		border = t.style.Box.BottomRight
 	} else if hint.isSeparatorRow {
-		if t.shouldMergeCellsVertically(t.numColumns-1, hint) {
+		if t.shouldMergeCellsVerticallyAbove(t.numColumns-1, hint) {
 			border = t.style.Box.Right
 		} else {
 			border = t.style.Box.RightSeparator
@@ -522,12 +522,12 @@ func (t *Table) getColumnSeparator(row rowStr, colIdx int, hint renderHint) stri
 }
 
 func (t *Table) getColumnSeparatorNonBorder(mergeCellsAbove bool, mergeCellsBelow bool, colIdx int, hint renderHint) string {
-	mergeNextCol := t.shouldMergeCellsVertically(colIdx, hint)
+	mergeNextCol := t.shouldMergeCellsVerticallyAbove(colIdx, hint)
 	if hint.isAutoIndexColumn {
 		return t.getColumnSeparatorNonBorderAutoIndex(mergeNextCol, hint)
 	}
 
-	mergeCurrCol := t.shouldMergeCellsVertically(colIdx-1, hint)
+	mergeCurrCol := t.shouldMergeCellsVerticallyAbove(colIdx-1, hint)
 	return t.getColumnSeparatorNonBorderNonAutoIndex(mergeCellsAbove, mergeCellsBelow, mergeCurrCol, mergeNextCol)
 }
 
@@ -836,7 +836,7 @@ func (t *Table) shouldMergeCellsHorizontallyBelow(row rowStr, colIdx int, hint r
 	return false
 }
 
-func (t *Table) shouldMergeCellsVertically(colIdx int, hint renderHint) bool {
+func (t *Table) shouldMergeCellsVerticallyAbove(colIdx int, hint renderHint) bool {
 	if !t.firstRowOfPage && t.columnConfigMap[colIdx].AutoMerge && colIdx < t.numColumns {
 		if hint.isSeparatorRow {
 			rowPrev := t.getRow(hint.rowNumber-1, hint)
@@ -855,6 +855,23 @@ func (t *Table) shouldMergeCellsVertically(colIdx int, hint renderHint) bool {
 	return false
 }
 
+func (t *Table) shouldMergeCellsVerticallyBelow(colIdx int, hint renderHint) int {
+	numRowsToMerge := 0
+	if t.columnConfigMap[colIdx].AutoMerge && colIdx < t.numColumns {
+		numRowsToMerge = 1
+		rowCurr := t.getRow(hint.rowNumber-1, hint)
+		for rowIdx := hint.rowNumber; rowIdx < len(t.rows); rowIdx++ {
+			rowNext := t.getRow(rowIdx, hint)
+			if colIdx < len(rowCurr) && colIdx < len(rowNext) && rowNext[colIdx] == rowCurr[colIdx] {
+				numRowsToMerge++
+			} else {
+				break
+			}
+		}
+	}
+	return numRowsToMerge
+}
+
 func (t *Table) shouldSeparateRows(rowIdx int, numRows int) bool {
 	// not asked to separate rows and no manually added separator
 	if !t.style.Options.SeparateRows && !t.separators[rowIdx] {