use gonum style formatter

Author: soypat

formatter.go

@@ -45,11 +45,146 @@ func (f formatter) Format(fs fmt.State, c rune) {
 		return
 	}
 	if f.format == nil {
-		f.format = formatMATLAB
+		f.format = format
 	}
 	f.format(f.matrix, f.prefix, f.margin, f.dot, f.squeeze, fs, c)
 }
 
+// FormatMATLAB sets the printing behavior to output MATLAB syntax. If MATLAB syntax is
+// specified, the ' ' verb flag and Excerpt option are ignored. If the alternative syntax
+// verb flag, '#' is used the matrix is formatted in rows and columns.
+func FormatMATLAB() FormatOption {
+	return func(f *formatter) { f.format = formatMATLAB }
+}
+
+// format prints a pretty representation of m to the fs io.Writer. The format character c
+// specifies the numerical representation of elements; valid values are those for float64
+// specified in the fmt package, with their associated flags. In addition to this, a space
+// preceding a verb indicates that zero values should be represented by the dot character.
+// The printed range of the matrix can be limited by specifying a positive value for margin;
+// If margin is greater than zero, only the first and last margin rows/columns of the matrix
+// are output. If squeeze is true, column widths are determined on a per-column basis.
+//
+// format will not provide Go syntax output.
+func format(m Matrix, prefix string, margin int, dot byte, squeeze bool, fs fmt.State, c rune) {
+	rows, cols := m.Dims()
+
+	var printed int
+	if margin <= 0 {
+		printed = rows
+		if cols > printed {
+			printed = cols
+		}
+	} else {
+		printed = margin
+	}
+
+	prec, pOk := fs.Precision()
+	if !pOk {
+		prec = -1
+	}
+
+	var (
+		maxWidth int
+		widths   widther
+		buf, pad []byte
+	)
+	if squeeze {
+		widths = make(columnWidth, cols)
+	} else {
+		widths = new(uniformWidth)
+	}
+	switch c {
+	case 'v', 'e', 'E', 'f', 'F', 'g', 'G':
+		if c == 'v' {
+			buf, maxWidth = maxCellWidth(m, 'g', printed, prec, widths)
+		} else {
+			buf, maxWidth = maxCellWidth(m, c, printed, prec, widths)
+		}
+	default:
+		fmt.Fprintf(fs, "%%!%c(%T=Dims(%d, %d))", c, m, rows, cols)
+		return
+	}
+	width, _ := fs.Width()
+	width = max(width, maxWidth)
+	pad = make([]byte, max(width, 2))
+	for i := range pad {
+		pad[i] = ' '
+	}
+
+	first := true
+	if rows > 2*printed || cols > 2*printed {
+		first = false
+		fmt.Fprintf(fs, "Dims(%d, %d)\n", rows, cols)
+	}
+
+	skipZero := fs.Flag(' ')
+	for i := 0; i < rows; i++ {
+		if !first {
+			fmt.Fprint(fs, prefix)
+		}
+		first = false
+		var el string
+		switch {
+		case rows == 1:
+			fmt.Fprint(fs, "[")
+			el = "]"
+		case i == 0:
+			fmt.Fprint(fs, "⎡")
+			el = "⎤\n"
+		case i < rows-1:
+			fmt.Fprint(fs, "⎢")
+			el = "⎥\n"
+		default:
+			fmt.Fprint(fs, "⎣")
+			el = "⎦"
+		}
+
+		for j := 0; j < cols; j++ {
+			if j >= printed && j < cols-printed {
+				j = cols - printed - 1
+				if i == 0 || i == rows-1 {
+					fmt.Fprint(fs, "...  ...  ")
+				} else {
+					fmt.Fprint(fs, "          ")
+				}
+				continue
+			}
+
+			v := m.At(i, j)
+			if v == 0 && skipZero {
+				buf = buf[:1]
+				buf[0] = dot
+			} else {
+				if c == 'v' {
+					buf = strconv.AppendFloat(buf[:0], v, 'g', prec, 64)
+				} else {
+					buf = strconv.AppendFloat(buf[:0], v, byte(c), prec, 64)
+				}
+			}
+			if fs.Flag('-') {
+				fs.Write(buf)
+				fs.Write(pad[:widths.width(j)-len(buf)])
+			} else {
+				fs.Write(pad[:widths.width(j)-len(buf)])
+				fs.Write(buf)
+			}
+
+			if j < cols-1 {
+				fs.Write(pad[:2])
+			}
+		}
+
+		fmt.Fprint(fs, el)
+
+		if i >= printed-1 && i < rows-printed && 2*printed < rows {
+			i = rows - printed - 1
+			fmt.Fprintf(fs, "%s .\n%[1]s .\n%[1]s .\n", prefix)
+			continue
+		}
+	}
+}
+
 // formatMATLAB prints a MATLAB representation of m to the fs io.Writer. The format character c
 // specifies the numerical representation of elements; valid values are those for float64
 // specified in the fmt package, with their associated flags.