smarter autoheight for ordinal scales?

[Fil]

autoHeight with the default round:true option sometimes leaves too much white space. In the chart below it returns a value of 580, when ideally it should be 556px.

Plot.plot({
  x: {
    percent: true,
    label: "Frequency (%) →"
  },
  height: 556,
  y: {
    label: null
  },
  marks: [
    Plot.gridX({interval: 1}),
    Plot.axisX({anchor: "top"}),
    Plot.axisX({anchor: "bottom", label: null}),
    Plot.barX(alphabet, {x: "frequency", y: "letter", fill: "steelblue"}),
    Plot.ruleX([0])
  ]
})

[mbostock]

To do this, autoHeight needs to know whether the y-scale

• is band or point
• has rounding enabled
• has (outer) padding

Essentially it needs to replicate the internal logic of d3-scale. Though possibly we could use a similar technique to outerRange by setting the y-scale’s range and then querying it to see what it’s doing.

[Fil]

There is a related issue with the aspectRatio option (#837), where two band scales with aspectRatio:1 might result in an automatic height that would be appropriate if rounding was false, but with rounding, end up with slightly different values.

For example:

export async function aspectRatioBand() {
  const a = Plot.plot({
    grid: true,
    inset: 6,
    x: {type: "band", domain: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"},
    y: {type: "band", domain: [1]},
    aspectRatio: 1,
    marks: [
      Plot.frame(),
      Plot.cell(["A1", "B4", "F3", "E3", "B5"], {x: (d) => d[0], y: (d) => +d[1], fill: Plot.identity})
    ]
  });
  console.log(a.scale("x").bandwidth / a.scale("y").bandwidth);
  return a;
}

result in a ratio = 1.118