Error Bars

When to use

Error bars are an overlay added on top of an existing chart series. They are useful for:

Scientific plots showing measurement uncertainty or standard deviation.
Confidence intervals around model predictions.
Range indicators on any point-based chart.

Error bars implement the same Chart interface as other series, so they automatically expand the axis bounds to fit the full bar extent.

Symmetric error bars

Vaccine antibody titre measured at seven time points post-vaccination. Passing a single error slice draws symmetric ±σ bars.

package main

import (
	"github.com/goplotlib/goplotlib/chart"
	"github.com/goplotlib/goplotlib/plot"
)

func main() {
	// Days after second dose
	days  := []float64{7, 14, 21, 28, 42, 60, 90}
	// Mean antibody titre (AU/mL)
	titre := []float64{12.3, 48.7, 142.5, 215.8, 189.4, 143.2, 98.6}
	// Standard deviation (symmetric ±)
	sigma := []float64{3.1, 12.4, 28.9, 41.2, 35.7, 29.8, 22.1}

	fig := plot.New(plot.WithWidth(860), plot.WithHeight(420))
	ax := fig.AddAxes()
	ax.Scatter(days, titre, chart.ScatterStyle{Label: "mean titre", MarkerSize: 6})
	ax.ErrorBars(days, titre, sigma)
	ax.SetTitle("Antibody Response Post-Vaccination").
		SetXLabel("Days after dose").
		SetYLabel("Titre (AU/mL) ± σ")
}

Error bars

Asymmetric error bars

Pass a second slice for the upper bound when the uncertainty is not symmetric — for example, a 95 % confidence interval from a log-normal distribution:

// A/B test: conversion rate by variant with asymmetric 95% CI
variants := []float64{1, 2, 3, 4}
rates    := []float64{3.2, 4.1, 3.8, 4.7}
ciLow    := []float64{0.4, 0.5, 0.4, 0.6}
ciHigh   := []float64{0.6, 0.7, 0.5, 0.8}

ax.Scatter(variants, rates, chart.ScatterStyle{Label: "conversion %", MarkerSize: 7})
ax.ErrorBars(variants, rates, ciLow, ciHigh)

The bar extends from y − ciLow[i] to y + ciHigh[i].

Horizontal error bars

ax.ErrorBarsX(xs, ys, xErr) // symmetric ±xErr

Signature reference

// Vertical error bars. Pass one slice for symmetric ±yLow bars,
// or two slices for asymmetric lower/upper bounds.
func (a *Axes) ErrorBars(xs, ys, yLow []float64, yHigh ...[]float64) *Axes

// Horizontal error bars (symmetric).
func (a *Axes) ErrorBarsX(xs, ys, xErr []float64) *Axes

Error bars automatically inherit the color of the immediately preceding chart series.

Box Plot