stat-ellipse
Covariance-ellipse statistic: one ellipse per group from the sample covariance of (x, y).
Each output row carries the parameters that geom-ellipse expects: (x0, y0, a, b, angle) with x0, y0 the group centroid, a, b the semi-major and semi-minor radii in data units, and angle the rotation in radians. Pair with geom-ellipse(stat: stat-ellipse()) or equivalently geom-ellipse(stat: "ellipse").
Usage
stat-ellipse(
level: 0.95,
)Parameters
| Parameter | Default | Description |
|---|---|---|
level |
0.95 |
Coverage probability for the confidence ellipse, in (0, 1). |
Returns
Statistic object with name: "ellipse", consumed by geom-ellipse.
Outputs
x0.y0.a.b.angle.
Examples
Three Gaussian-like clusters, each enclosed by a 95% confidence ellipse.
#let pts = ()
#for (cx, cy, k) in ((0, 0, "a"), (4, 1, "b"), (2, 4, "c")) {
for i in range(0, 30) {
let r = (calc.sin(i * 0.7) + calc.cos(i * 1.1)) * 0.4
pts.push((
x: cx + calc.cos(i * 0.5) + r,
y: cy + calc.sin(i * 0.5) + r,
k: k,
))
}
}
#plot(
data: pts,
mapping: aes(x: "x", y: "y", fill: "k"),
layers: (
geom-point(size: 2pt),
geom-ellipse(stat: stat-ellipse(), alpha: 0.2),
),
width: 10cm,
height: 6cm,
)
