Could you add the possibility of semi circular pie chart ?

[Akilon27]

In (french) school, we sometimes use half disk pie charts (north half), as a teacher it would be useful to me. (I think they are sometimes called parliament charts.)

[johannes-wolf]

This is already included :) You can use the start: <angle> and stop: <angle> arguments.

Example:

#import "@preview/cetz:0.5.2"
#import "@preview/cetz-plot:0.1.4": chart

#set page(width: auto, height: auto, margin: .5cm)

#let data = (
  ([Belgium],     24),
  ([Germany],     31),
  ([Greece],      18),
  ([Spain],       21),
  ([France],      23),
  ([Hungary],     18),
  ([Netherlands], 27),
  ([Romania],     17),
  ([Finland],     26),
  ([Turkey],      13),
)

#cetz.canvas({
  let colors = gradient.linear(red, blue, green, yellow)

  chart.piechart(
    data,
    value-key: 1,
    label-key: none,
    radius: 4,
    stroke: none,
    slice-style: colors,
    inner-radius: 1,
    outset: 3,
    start: 0deg,
    stop: 180deg,
    inner-label: (content: (value, label) => [#text(white, str(value))], radius: 110%),
    outer-label: (content: "%", radius: 110%))
})

[Akilon27]

I have no idea why I didn't try that ! Maybe it could be added to the manual but it should have been something obvious to try...

Unrelated but I add to look at https://github.com/cetz-package/cetz-plot/blob/master/src/chart/piechart.typ to see in the default-style how to style the legend : it doesn't appear in the manual.