BarChart error: invalid data range; cannot be zero

[panicake]

When I get one value or a series of same value, and draw a BarChart, I will get an error 'invalid data range; cannot be zero'.
Finally, I found the reason.

yr = bc.getRanges()
	if yr.GetMax()-yr.GetMin() == 0 {
		return fmt.Errorf("invalid data range; cannot be zero")
	}

In the function getRanges，when one value or a series of same valuebc.Bars，min and max is same all the time. As a result, program will throw an error 'invalid data range; cannot be zero'.

min, max := math.MaxFloat64, -math.MaxFloat64
	for _, b := range bc.Bars {
		min = math.Min(b.Value, min)
		max = math.Max(b.Value, max)
	}

[panicake]

I fixed this problem by rewriting code like this:

if yr.GetMax()-yr.GetMin() == 0 {
		// return fmt.Errorf("invalid data range; cannot be zero")
		v := yr.GetMax()
		if v > 0 {
			yr.SetMin(0)
		} else if  v < 0 {
			yr.SetMax(0)
		} else {
			yr.SetMax(0.5)
			yr.SetMin(0)
		}
	}

[panicake]

in bar_chart.go

[FrontSide]

Hey @lovermaker. Thanks for this. I'd be interested in seeing that merged. Would you be able to open A PR?

[daill]

Faced this problem too and used the implementation of @lovermaker, works like a charm. I guess this should be merged soon.

[malaya7]

This Also worked for me, can someone merge this ?

[Grehgous]

For anyone unable to add a fork that has the fix proposed above, here is a workaround that can be added to your package that consumes go-chart.

func foo(graph chart.BarChart) {

	err := graph.Render(chart.PNG, buffer)

	// If there is a range error from go-chart, fix it and try it again.
	// Workaround for https://github.com/wcharczuk/go-chart/issues/62
	if err != nil && err.Error() == "invalid data range; cannot be zero" {
		fixRange(&graph)
		err = graph.Render(chart.PNG, buffer)
	}

	if err != nil {
		return nil, err
	}
}

// fixRange is a workaround for a go-chart issue where graph generation errors out if min and max yVals are equal.
// Workaround based off proposed fix from this ticket https://github.com/wcharczuk/go-chart/issues/62
func fixRange(graph *chart.BarChart) {

	var yRange chart.Range

	if graph.YAxis.Range != nil && !graph.YAxis.Range.IsZero() {
		yRange = graph.YAxis.Range
	} else {
		yRange = &chart.ContinuousRange{}
	}

	max := yRange.GetMax()

	// Min and max are different, no work needed
	if max-yRange.GetMin() != 0 {
		return
	}

	// Adjust range so min and max are different
	if max > 0 {
		yRange.SetMin(0)
	} else if max < 0 {
		yRange.SetMax(0)
	} else {
		yRange.SetMax(0.5)
		yRange.SetMin(0)
	}

	graph.YAxis.Range = yRange
}

Hopefully this ticket gets some attention. It has been a long standing issue and has a simple fix.