ncdu: add toggle option for average size in directory - key 'a'

Add toggle option to show average size in directory. This toggle
function is for ncdu and is binded to key 'a'.

cmd/ncdu/ncdu.go

@@ -71,6 +71,7 @@ func helpText() (tr []string) {
 		" ←,h to return",
 		" c toggle counts",
 		" g toggle graph",
+		" a toggle average size in directory",
 		" n,s,C,A sort by name,size,count,average size",
 		" d delete file/directory",
 	}
@@ -105,6 +106,7 @@ type UI struct {
 	listing            bool          // whether listing is in progress
 	showGraph          bool          // toggle showing graph
 	showCounts         bool          // toggle showing counts
+	showDirAverageSize bool          // toggle average size
 	sortByName         int8          // +1 for normal, 0 for off, -1 for reverse
 	sortBySize         int8
 	sortByCount        int8
@@ -346,6 +348,18 @@ func (u *UI) Draw() error {
 					extras += "         "
 				}
 
+			}
+			var averageSize float64
+			if count > 0 {
+				averageSize = float64(size) / float64(count)
+			}
+			if u.showDirAverageSize {
+				if averageSize > 0 {
+					extras += fmt.Sprintf("%8v ", fs.SizeSuffix(int64(averageSize)))
+				} else {
+					extras += "         "
+				}
+
 			}
 			if u.showGraph {
 				bars := (size + perBar/2 - 1) / perBar
@@ -667,6 +681,7 @@ func NewUI(f fs.Fs) *UI {
 		fsName:             f.Name() + ":" + f.Root(),
 		showGraph:          true,
 		showCounts:         false,
+		showDirAverageSize: false,
 		sortByName:         0, // +1 for normal, 0 for off, -1 for reverse
 		sortBySize:         1,
 		sortByCount:        0,
@@ -758,6 +773,8 @@ outer:
 					u.showCounts = !u.showCounts
 				case 'g':
 					u.showGraph = !u.showGraph
+				case 'a':
+					u.showDirAverageSize = !u.showDirAverageSize
 				case 'n':
 					u.toggleSort(&u.sortByName)
 				case 's':