Merging behavior on Footer

[EppO]

Hi,

Thanks for this awesome library, I love it!
I run into a cosmetic issue though, I would like to be able to merge the cells in the footer like I want.
I can do it when the merged columns are first, but not when they're last.
Here is an example:

┌─────────────┬──────────┬───────────────┬─────────┐
│ DEPARTMENT  │ DIVISION │     TEAM      │  LEAD   │
├─────────────┼──────────┼───────────────┼─────────┤
│ Engineering │ Backend  │ API Team      │ Alice   │
│             │          ├───────────────┼─────────┤
│             │          │ Database Team │ Bob     │
│             ├──────────┼───────────────┼─────────┤
│             │ Frontend │ UI Team       │ Charlie │
├─────────────┼──────────┼───────────────┼─────────┤
│ Marketing   │ Digital  │ SEO Team      │ Dave    │
│             │          ├───────────────┼─────────┤
│             │          │ Content Team  │ Eve     │
├─────────────┴──────────┴───────────────┼─────────┤
│                            Total Teams │       5 │
└────────────────────────────────────────┴─────────┘

the first 2 "empty" columns are getting merged with the first non-empty one table.Footer([]string{"", "", "Total Teams", "5"})

in that example:

┌─────────────┬──────────┬───────────────┬─────────┐
│ DEPARTMENT  │ DIVISION │     TEAM      │  LEAD   │
├─────────────┼──────────┼───────────────┼─────────┤
│ Engineering │ Backend  │ API Team      │ Alice   │
│             │          ├───────────────┼─────────┤
│             │          │ Database Team │ Bob     │
│             ├──────────┼───────────────┼─────────┤
│             │ Frontend │ UI Team       │ Charlie │
├─────────────┼──────────┼───────────────┼─────────┤
│ Marketing   │ Digital  │ SEO Team      │ Dave    │
│             │          ├───────────────┼─────────┤
│             │          │ Content Team  │ Eve     │
├─────────────┼──────────┼───────────────┼─────────┤
│ Total Teams │        5 │               │         │
└─────────────┴──────────┴───────────────┴─────────┘

the 3 last columns are not merged at all table.Footer([]string{"Total Teams", "5"})

here is the complete code to reproduce:

package main

import (
 "os"

 "github.com/olekukonko/tablewriter"
 "github.com/olekukonko/tablewriter/renderer"
 "github.com/olekukonko/tablewriter/tw"
)

func main() {
 data := [][]string{
  {"Engineering", "Backend", "API Team", "Alice"},
  {"Engineering", "Backend", "Database Team", "Bob"},
  {"Engineering", "Frontend", "UI Team", "Charlie"},
  {"Marketing", "Digital", "SEO Team", "Dave"},
  {"Marketing", "Digital", "Content Team", "Eve"},
 }

 table := tablewriter.NewTable(os.Stdout,
  tablewriter.WithRenderer(renderer.NewBlueprint(tw.Rendition{
   Settings: tw.Settings{Separators: tw.Separators{BetweenRows: tw.On}},
  })),
  tablewriter.WithConfig(tablewriter.Config{
   Header: tw.CellConfig{Alignment: tw.CellAlignment{Global: tw.AlignCenter}},
   Row: tw.CellConfig{
    Formatting: tw.CellFormatting{MergeMode: tw.MergeHierarchical},
    Alignment:  tw.CellAlignment{Global: tw.AlignLeft},
   },
   Footer: tw.CellConfig{
    Formatting: tw.CellFormatting{
     MergeMode: tw.MergeHorizontal,
    },
   },
  }),
 )
 table.Header([]string{"Department", "Division", "Team", "Lead"})
 table.Bulk(data)
 table.Footer([]string{"Total Teams", "5"})
 table.Render()
}

[EppO]

I found a workaround repeating the value I want to merge in the other columns like so:

package main

import (
 "os"

 "github.com/olekukonko/tablewriter"
 "github.com/olekukonko/tablewriter/renderer"
 "github.com/olekukonko/tablewriter/tw"
)

func main() {
 data := [][]string{
  {"Engineering", "Backend", "API Team", "Alice"},
  {"Engineering", "Backend", "Database Team", "Bob"},
  {"Engineering", "Frontend", "UI Team", "Charlie"},
  {"Marketing", "Digital", "SEO Team", "Dave"},
  {"Marketing", "Digital", "Content Team", "Eve"},
 }

 table := tablewriter.NewTable(os.Stdout,
  tablewriter.WithRenderer(renderer.NewBlueprint(tw.Rendition{
   Settings: tw.Settings{Separators: tw.Separators{BetweenRows: tw.On}},
  })),
  tablewriter.WithConfig(tablewriter.Config{
   Header: tw.CellConfig{Alignment: tw.CellAlignment{Global: tw.AlignCenter}},
   Row: tw.CellConfig{
    Formatting: tw.CellFormatting{MergeMode: tw.MergeHierarchical},
    Alignment:  tw.CellAlignment{Global: tw.AlignLeft},
   },
   Footer: tw.CellConfig{
    Alignment: tw.CellAlignment{Global: tw.AlignLeft},
    Formatting: tw.CellFormatting{
     MergeMode: tw.MergeHorizontal,
    },
   },
  }),
 )
 table.Header([]string{"Department", "Division", "Team", "Lead"})
 table.Bulk(data)
 table.Footer([]string{"Total Teams", "5", "5", "5"})
 table.Render()
}

but in that case, it doesn't follow the specified alignment AlignLeft:

┌─────────────┬──────────┬───────────────┬─────────┐
│ DEPARTMENT  │ DIVISION │     TEAM      │  LEAD   │
├─────────────┼──────────┼───────────────┼─────────┤
│ Engineering │ Backend  │ API Team      │ Alice   │
│             │          ├───────────────┼─────────┤
│             │          │ Database Team │ Bob     │
│             ├──────────┼───────────────┼─────────┤
│             │ Frontend │ UI Team       │ Charlie │
├─────────────┼──────────┼───────────────┼─────────┤
│ Marketing   │ Digital  │ SEO Team      │ Dave    │
│             │          ├───────────────┼─────────┤
│             │          │ Content Team  │ Eve     │
├─────────────┼──────────┴───────────────┴─────────┤
│ Total Teams │                                  5 │
└─────────────┴────────────────────────────────────┘

If I remove the MergeHorizontal setting, I can see the repeated values have the correct alignment, there seems to be a bug when MergeHorizontal is involved in the alignment calculation

[EppO]

Running in debug, I see these interesting logs:

[table/blueprint] DEBUG: Starting Footer render: IsSubRow=false, Location=end, Pos=footer
[table/blueprint] DEBUG: renderLine: Prefix='│' (f.width 1)
[table/blueprint] DEBUG: renderLine: Regular col 0, visualWidth 13
[table/blueprint] DEBUG: Formatting cell: content='Total Teams', width=13, align=left, padding={L:' ' R:' '}
[table/blueprint] DEBUG: Available content width: 11
[table/blueprint] DEBUG: Total padding width: 2
[table/blueprint] DEBUG: Applied right padding: ' ' for 1 width
[table/blueprint] DEBUG: Formatted cell final result: ' Total Teams ' (target width 13)
[table/blueprint] DEBUG: renderLine: Rendered col 0, formattedCell=' Total Teams ' (f.width 13), totalLineWidth=14
[table/blueprint] DEBUG: renderLine: Rendered regular col 0 (visualWidth 13, align left): ' Total Teams '
[table/blueprint] DEBUG: renderLine: Added separator '│' before col 1 (f.width 1)
[table/blueprint] DEBUG: renderLine: H/F HMerge col 1, span 3, pre-adjusted visualWidth 36
[table/blueprint] DEBUG: renderLine: Applying AlignRight HMerge/TOTAL override for Footer col 1. Original/default align was: left
[table/blueprint] DEBUG: Formatting cell: content='5', width=36, align=right, padding={L:' ' R:' '}
[table/blueprint] DEBUG: Available content width: 34
[table/blueprint] DEBUG: Total padding width: 35
[table/blueprint] DEBUG: Applied left padding: ' ' for 34 width
[table/blueprint] DEBUG: Formatted cell final result: '                                  5 ' (target width 36)
[table/blueprint] DEBUG: renderLine: Rendered col 1, formattedCell='                                  5 ' (f.width 36), totalLineWidth=51
[table/blueprint] DEBUG: renderLine: Rendered HMerge START col 1 (span 3, visualWidth 36, align right): '                                  5 '
[table/blueprint] DEBUG: renderLine: Suffix='│' (f.width 1)
[table/blueprint] DEBUG: renderLine: Final rendered line: '│ Total Teams │                                  5 │' (total width 52)
[table/blueprint] DEBUG: Completed Footer render

It states Original/default align was: left but it overrides it Applying AlignRight HMerge as the following line says align=right.
Then it applies the left padding but I assume it's because it's in right alignment mode.
Why does the horizontal merge switches the alignment to right only?

[olekukonko]

Hi @EppO, thanks for pointing this out.

As you can see, the message states:
Applying AlignRight HMerge/TOTAL override for Footer col 1. Original/default align was: left.

This was part of the initial behavior defined for merged cells in the footer. However, I've decided to update the logic so that the override is now only applied when align == tw.AlignNone.

With this update

package main

import (
	"os"

	"github.com/olekukonko/tablewriter"
	"github.com/olekukonko/tablewriter/renderer"
	"github.com/olekukonko/tablewriter/tw"
)

func main() {
	data := [][]string{
		{"Engineering", "Backend", "API Team", "Alice"},
		{"Engineering", "Backend", "Database Team", "Bob"},
		{"Engineering", "Frontend", "UI Team", "Charlie"},
		{"Marketing", "Digital", "SEO Team", "Dave"},
		{"Marketing", "Digital", "Content Team", "Eve"},
	}

	table := tablewriter.NewTable(os.Stdout,
		tablewriter.WithRenderer(renderer.NewBlueprint(tw.Rendition{
			Settings: tw.Settings{Separators: tw.Separators{BetweenRows: tw.On}},
		})),
		tablewriter.WithConfig(tablewriter.Config{
			Header: tw.CellConfig{Alignment: tw.CellAlignment{Global: tw.AlignCenter}},
			Row: tw.CellConfig{
				Formatting: tw.CellFormatting{MergeMode: tw.MergeHierarchical},
				Alignment:  tw.CellAlignment{Global: tw.AlignLeft},
			},
			Footer: tw.CellConfig{
				Alignment: tw.CellAlignment{Global: tw.AlignLeft},
				Formatting: tw.CellFormatting{
					MergeMode: tw.MergeHorizontal,
				},
			},
			Debug: true,
		}),
	)
	table.Header([]string{"Department", "Division", "Team", "Lead"})
	table.Bulk(data)
	table.Footer([]string{"Total", "5", "5", "5"})
	table.Render()
}

output

┌─────────────┬──────────┬───────────────┬─────────┐
│ DEPARTMENT  │ DIVISION │     TEAM      │  LEAD   │
├─────────────┼──────────┼───────────────┼─────────┤
│ Engineering │ Backend  │ API Team      │ Alice   │
│             │          ├───────────────┼─────────┤
│             │          │ Database Team │ Bob     │
│             ├──────────┼───────────────┼─────────┤
│             │ Frontend │ UI Team       │ Charlie │
├─────────────┼──────────┼───────────────┼─────────┤
│ Marketing   │ Digital  │ SEO Team      │ Dave    │
│             │          ├───────────────┼─────────┤
│             │          │ Content Team  │ Eve     │
├─────────────┼──────────┴───────────────┴─────────┤
│ Total       │ 5                                  │
└─────────────┴────────────────────────────────────┘

[EppO]

That's exactly what I wanted to achieve! Thank you so much for the quick fix!
One very last thing I wanted to discuss to make that library perfect: vertical alignment. To make it look like

┌─────────────┬──────────┬───────────────┬─────────┐
│ DEPARTMENT  │ DIVISION │     TEAM      │  LEAD   │
├─────────────┼──────────┼───────────────┼─────────┤
│             │          │ API Team      │ Alice   │
│             │ Backend  ├───────────────┼─────────┤
│ Engineering │          │ Database Team │ Bob     │
│             ├──────────┼───────────────┼─────────┤
│             │ Frontend │ UI Team       │ Charlie │
├─────────────┼──────────┼───────────────┼─────────┤
│             │          │ SEO Team      │ Dave    │
│  Marketing  │ Digital  ├───────────────┼─────────┤
│             │          │ Content Team  │ Eve     │
├─────────────┼──────────┴───────────────┴─────────┤
│ Total       │ 5                                  │
└─────────────┴────────────────────────────────────┘

I don't think that's possible today.
Would like me to open another issue to track as feature request?

[olekukonko]

I initially explored vertical alignment but discovered it was expensive. To properly center text vertically in merged cells, the renderer must know the total visual height of the span before rendering the first line requiring multiple passes and heavy use of buffered iterators.

To optimize this, I implemented olekukonko/it, which enabled lookahead ("peeking") without consuming the iterator. While functional, Introduced significant complexity hence I deemed the trade-off unjustified .

Logical vs. Visual Height Mismatch

┌─────────────┬──────────┬───────────────┬─────────┐
│ ...         │ ...      │ ...           │ ...     │
├─────────────┼──────────┼───────────────┼─────────┤
│             │          │ API Team      │ Alice   │
│ Engineering │ Backend  ├───────────────┼─────────┤  <-- The text "Engineering" is vertically centered
│             │          │ Database Team │ Bob     │
├─────────────┼──────────┼───────────────┼─────────┤
│             │ Frontend │ UI Team       │ Charlie │
└─────────────┴──────────┴───────────────┴─────────┘

┌─────────────┬──────────┬───────────────────┬─────────┐
│             │          │ This is a long    │ Alice   │
│             │          │ description for   │         │
│             │          │ the API team that │         │
│ Engineering │ Backend  │ wraps to 3 lines. │         │
│             │          ├───────────────────┼─────────┤
│             │          │ Database Team     │ Bob     │
│             ├──────────┼───────────────────┼─────────┤
│             │ Frontend │ UI Team           │ Charlie │
└─────────────┴──────────┴───────────────────┴─────────┘

• applyVerticalMerges|applyHierarchicalMerges knows a cell spans N logical rows but not their visual height due to word-wrapping
• Example: One row in a merge might be 1 line tall, while another spans 3 lines due to wrapped text in another column.
• Without multi-pass logic to precompute total visual height, alignment remains inconsistent.
• Determining box-drawing characters (┴, ┬, ├, ┤, ┼) during merges is nontrivial.
• We have to Introduce state-aware batch rendering (e.g., pre-calculating visual heights).
• Redesign interfaces to handle multi-pass logic without breaking existing integrations.

This risks breaking changes, especially in the renderer’s public functions & interface, major reimplementation, and careful versioning to avoid something like #270 happening again. Hence i believe, simplicity and performance take precedence over edge-case alignment. If demand grows, we could revisit this.

[EppO]

That's completely fair. Thank you for taking the time to provide such clear and thorough explanation. Really appreciate it!
I will close that comment when 1.0.9 is out