table: suppress empty columns if asked to; fixes #124 (#126)

table/README.md

@@ -20,6 +20,7 @@ Pretty-print tables into ASCII/Unicode strings.
     - Custom (vertical) VAlign per column with multi-line cell support (`ColumnConfig.VAlign*`)
   - Mirror output to an `io.Writer` (ex. `os.StdOut`) (`SetOutputMirror`)
   - Sort by one or more Columns (`SortBy`)
+  - Suppress/hide columns with no content (`SuppressEmptyColumns`) 
   - Customizable Cell rendering per Column (`ColumnConfig.Transformer*`)
   - Hide any columns that you don't want displayed (`ColumnConfig.Hidden`)
   - Reset Headers/Rows/Footers at will to reuse the same Table Writer (`Reset*`)

table/render_test.go

@@ -1140,6 +1140,44 @@ func TestTable_Render_Styles(t *testing.T) {
 	}
 }
 
+func TestTable_Render_SuppressEmptyColumns(t *testing.T) {
+	tw := NewWriter()
+	tw.AppendHeader(testHeader)
+	tw.AppendRows([]Row{
+		{1, "Arya", "", 3000},
+		{20, "Jon", "", 2000, "You know nothing, Jon Snow!"},
+		{300, "Tyrion", "", 5000},
+	})
+	tw.AppendRow(Row{11, "Sansa", "", 6000})
+	tw.AppendFooter(Row{"", "", "TOTAL", 10000})
+	tw.SetStyle(StyleLight)
+
+	expectedOut := `┌─────┬────────────┬───────────┬────────┬─────────────────────────────┐
+│   # │ FIRST NAME │ LAST NAME │ SALARY │                             │
+├─────┼────────────┼───────────┼────────┼─────────────────────────────┤
+│   1 │ Arya       │           │   3000 │                             │
+│  20 │ Jon        │           │   2000 │ You know nothing, Jon Snow! │
+│ 300 │ Tyrion     │           │   5000 │                             │
+│  11 │ Sansa      │           │   6000 │                             │
+├─────┼────────────┼───────────┼────────┼─────────────────────────────┤
+│     │            │ TOTAL     │  10000 │                             │
+└─────┴────────────┴───────────┴────────┴─────────────────────────────┘`
+	assert.Equal(t, expectedOut, tw.Render())
+
+	tw.SuppressEmptyColumns()
+	expectedOut = `┌─────┬────────────┬────────┬─────────────────────────────┐
+│   # │ FIRST NAME │ SALARY │                             │
+├─────┼────────────┼────────┼─────────────────────────────┤
+│   1 │ Arya       │   3000 │                             │
+│  20 │ Jon        │   2000 │ You know nothing, Jon Snow! │
+│ 300 │ Tyrion     │   5000 │                             │
+│  11 │ Sansa      │   6000 │                             │
+├─────┼────────────┼────────┼─────────────────────────────┤
+│     │            │  10000 │                             │
+└─────┴────────────┴────────┴─────────────────────────────┘`
+	assert.Equal(t, expectedOut, tw.Render())
+}
+
 func TestTable_Render_TableWithinTable(t *testing.T) {
 	twInner := NewWriter()
 	twInner.AppendHeader(testHeader)

table/table.go

@@ -94,6 +94,9 @@ type Table struct {
 	sortBy []SortBy
 	// style contains all the strings used to draw the table, and more
 	style *Style
+	// suppressEmptyColumns hides columns which have no content on all regular
+	// rows
+	suppressEmptyColumns bool
 	// title contains the text to appear above the table
 	title string
 }
@@ -278,6 +281,12 @@ func (t *Table) Style() *Style {
 	return t.style
 }
 
+// SuppressEmptyColumns hides columns when the column is empty in ALL the
+// regular rows.
+func (t *Table) SuppressEmptyColumns() {
+	t.suppressEmptyColumns = true
+}
+
 func (t *Table) analyzeAndStringify(row Row, hint renderHint) rowStr {
 	// update t.numColumns if this row is the longest seen till now
 	if len(row) > t.numColumns {
@@ -699,6 +708,9 @@ func (t *Table) initForRenderRows() {
 	// sort the rows as requested
 	t.initForRenderSortRows()
 
+	// suppress columns without any content
+	t.initForRenderSuppressColumns()
+
 	// strip out hidden columns
 	t.initForRenderHideColumns()
 }
@@ -761,6 +773,27 @@ func (t *Table) initForRenderSortRows() {
 	}
 }
 
+func (t *Table) initForRenderSuppressColumns() {
+	shouldSuppressColumn := func(colIdx int) bool {
+		for _, row := range t.rows {
+			if colIdx < len(row) && row[colIdx] != "" {
+				return false
+			}
+		}
+		return true
+	}
+
+	if t.suppressEmptyColumns {
+		for colIdx := 0; colIdx < t.numColumns; colIdx++ {
+			if shouldSuppressColumn(colIdx) {
+				cc := t.columnConfigMap[colIdx]
+				cc.Hidden = true
+				t.columnConfigMap[colIdx] = cc
+			}
+		}
+	}
+}
+
 func (t *Table) isIndexColumn(colIdx int, hint renderHint) bool {
 	return t.indexColumn == colIdx+1 || hint.isAutoIndexColumn
 }

table/writer.go

@@ -31,6 +31,7 @@ type Writer interface {
 	SetTitle(format string, a ...interface{})
 	SortBy(sortBy []SortBy)
 	Style() *Style
+	SuppressEmptyColumns()
 
 	// deprecated; in favor of Style().HTML.CSSClass
 	SetHTMLCSSClass(cssClass string)