Function binPoints

plotter/histogram.go:185–223

binPoints returns a slice containing the given number of bins, and the width of each bin. If the given number of bins is not positive then a reasonable default is used. The default is the square root of the sum of the y values.

(xys XYer, n int)

// default is the square root of the sum of
// the y values.
func binPoints(xys XYer, n int) (bins []HistogramBin, width float64) {
	xmin, xmax := Range(XValues{xys})
	if n <= 0 {
		m := 0.0
		for i := range xys.Len() {
			_, y := xys.XY(i)
			m += math.Max(y, 1.0)
		}
		n = int(math.Ceil(math.Sqrt(m)))
	}
	if n < 1 || xmax <= xmin {
		n = 1
	}

	bins = make([]HistogramBin, n)

	w := (xmax - xmin) / float64(n)
	if w == 0 {
		w = 1
	}
	for i := range bins {
		bins[i].Min = xmin + float64(i)*w
		bins[i].Max = xmin + float64(i+1)*w
	}

	for i := range xys.Len() {
		x, y := xys.XY(i)
		bin := int((x - xmin) / w)
		if x == xmax {
			bin = n - 1
		}
		if bin < 0 || bin >= n {
			panic(fmt.Sprintf("%g, xmin=%g, xmax=%g, w=%g, bin=%d, n=%d\n",
				x, xmin, xmax, w, bin, n))
		}
		bins[bin].Weight += y
	}
	return bins, w
}

// A HistogramBin approximates the number of values
// within a range by a single number (the weight).