Bar and Rect Marks

Bar marks encode a numeric interval against a categorical or positional channel. Rect marks encode independent x and y intervals and are the general primitive for heatmaps, interval blocks, and cells.

import { scaleBand } from 'd3-scale'
import { barX, barY, cell, rect } from '@tanstack/charts'

barY#

barY draws vertical bars from y1 to y2 at x.

const mark = barY(rows, {
  x: 'category',
  y: 'value',
  key: 'id',
})

function barY<TDatum>(
  source: Iterable<TDatum>,
  options?: BarYOptions<TDatum>,
): ChartMark<TDatum, InferredX, number>

Options#

The interaction point is at the group-band center and the y2/y endpoint. Its semantic xValue is x and its yValue is the value endpoint.

barX#

barX draws horizontal bars from x1 to x2 at y.

const mark = barX(rows, {
  x: 'value',
  y: 'category',
  key: 'id',
})

function barX<TDatum>(
  source: Iterable<TDatum>,
  options?: BarXOptions<TDatum>,
): ChartMark<TDatum, number, InferredY>

Its options transpose barY:

The interaction point is at the x2/x endpoint and group-band center.

Bar bandwidth#

With a band scale on the categorical axis, bars use its responsive bandwidth. With a nonband scale, the mark estimates width from the smallest distance between distinct mapped positions and uses 80 percent of that distance. A single-position fallback is capped at 48 pixels.

For predictable categorical bars, use a configured band scale and set its padding. Scale setup and ownership are documented in Scales and D3.

inset is applied after band or inferred layout and is clamped to at least zero. A sufficiently large inset produces a zero-width or zero-height bar rather than negative geometry.

Grouped bars#

Pass a band-scale factory to infer its domain from non-null z values:

barY(rows, {
  x: 'quarter',
  y: 'revenue',
  z: 'region',
  groupScale: () => scaleBand<string>().padding(0.1),
})

TanStack Charts creates the scale and assigns [0, categoricalBandwidth] as its range. Pass a configured scale instance when subgroup order is fixed independently of the rendered rows.

The mark throws when:

• the scale has no bandwidth method
• a grouped row has a null z
• a z value is outside the group-scale domain or maps to a nonfinite position

z controls bar placement and interaction grouping. color may point at a different field when grouping and color semantics differ.

Bar baselines and invalid rows#

Omitting y1 or x1 uses zero and emits an includeZero scale hint. An explicit baseline, including a constant zero, removes the hint. The configured scale still owns its semantic domain.

Rows are skipped when their category, baseline, or endpoint is invalid. Negative and reversed intervals are supported because geometry uses the minimum mapped endpoint and absolute length.

rect#

rect draws one independent x/y interval per valid row:

const mark = rect(events, {
  x1: 'start',
  x2: 'end',
  y: 'lane',
  z: 'status',
  key: 'id',
})

function rect<TDatum>(
  source: Iterable<TDatum>,
  options: RectOptions<TDatum>,
): ChartMark<
  TDatum,
  InferredPointX,
  InferredPointY,
  InferredScaleX,
  InferredScaleY
>

Options#

Both endpoints must be valid chart values. Endpoint order may be reversed.

When two semantic endpoints are equal and the resolved scale has bandwidth, the rect spans that complete band. Otherwise it spans the mapped endpoint distance. This lets x: 'column', y: 'row' create a heatmap cell without manually deriving boundaries.

The interaction coordinate is the geometric center before inset. Semantic point values use a valid x and y. An omitted x defaults to the row index; an invalid x falls back to x2. An omitted or invalid y falls back to y2 unless the datum itself is numeric. Scale typing still includes all interval endpoints, so a heterogeneous interval remains honest without widening interaction callbacks unnecessarily.

cell#

cell is rect without explicit endpoint options:

const mark = cell(rows, {
  x: 'weekday',
  y: 'week',
  z: 'bucket',
  fillOpacity: 0.9,
})

type CellOptions<TDatum> = Omit<RectOptions<TDatum>, 'x1' | 'x2' | 'y1' | 'y2'>

Both axes normally use band scales. cell shares rect rendering, defaults, focus behavior, and class names.