Bar Chart

Bar charts are the workhorse for discrete categorical comparison — one quantitative value per category, read by length.

Vertical bars

The spec:

What this chart does well

Bars are the most honest choice when the x-axis is genuinely categorical: months, products, regions, event types. The reader’s eye compares lengths from a shared baseline, which is the comparison the visual system is best at. Length-from-zero is roughly the only chart primitive humans read accurately without practice.

They’re the wrong pick when the x-axis is continuous (line or area carries the trend better), when there are too many categories to read individually (consider a strip plot or a sorted lollipop), or when the story is part-to-whole composition (pie at small slice counts, otherwise stacked bar — planned for a later release).

Encoding reference

Channel	Required	Accepted types	Notes
x	yes	one of x/y must be categorical, the other quantitative	The categorical channel becomes the band axis; the quantitative channel becomes the value axis.
y	yes	same as above	Swaps role with x under orientation: 'horizontal'.
color	no	categorical	Sets per-bar colour, not series split. The palette wraps above ~20 distinct values; pixi-charts logs a console warning when that happens.

size and value are not used by bar charts.

See ChartEncoding and ChartOptions for the full type shapes (including orientation), or BarChart for the imperative API.

Horizontal bars

Use options.orientation: 'horizontal' when category labels are long enough to clip under vertical bars — product names, full sentences, multi-word region names. The band axis moves to the y-axis and each label sits on its own row.

The spec:

Notes

• Single series — v0.1 ships one bar per category. Grouped and stacked bars are planned.
• Negative values — the baseline sits at valueAdapter.scale(0), not the plot floor, so bars with negative values grow opposite the positive direction from a shared zero.
• Bar order — bars render in input-data order. Sort upstream if you want ranked output.
• Color = per-bar — unlike line and area, the color encoding in a bar chart paints each individual bar, not a series. Useful for highlighting a subset (e.g. a single quarter, or one tier of a categorical breakdown).