sort.go
func column(s string, n int) (int, string) {
	if n == 0 {
		return 0, s
	}
	currentColumn := 0
	wstart := -1
	for i, c := range s {
		sp := unicode.IsSpace(c)
		switch {
		case !sp && wstart < 0: // Start of word
			currentColumn++
			wstart = i
		case sp && wstart >= 0 && currentColumn == n: // End of nth col
			return 0, s[wstart:i]
		case sp && wstart >= 0: // End of another column
			wstart = -1
		}
	}
	if wstart >= 0 && currentColumn == n { // nth column ends string
		return 0, s[wstart:]
	}

	// col not found. Treat as a value smaller than all strings
	return -1, ""
}
func column(s string, n int) (int, string) {
	if n == 0 {
		return 0, s
	}
	currentColumn := 0
	wstart := -1
	for i, c := range s {
		sp := unicode.IsSpace(c)
		switch {
		case !sp && wstart < 0: // Start of word
			currentColumn++
			wstart = i
		case sp && wstart >= 0 && currentColumn == n: // End of nth col
			return 0, s[wstart:i]
		case sp && wstart >= 0: // End of another column
			wstart = -1
		}
	}
	if wstart >= 0 && currentColumn == n { // nth column ends string
		return 0, s[wstart:]
	}

	// col not found. Treat as a value smaller than all strings
	return -1, ""
}
// column(s, n) returns 0,x where x is the nth column (1-based) in s,
// or -1,"" if s does not have n columns.  A zero column number is
// treated specially: 0,s is returned.