stat-smooth
Smoother statistic: fitted curve with a pointwise confidence band.
Since 0.0.1.
Returns a dense grid of (x, y, ymin, ymax) rows where y is the fitted value and ymin/ymax bound a pointwise confidence band.
The loess band uses normal quantiles with the residual variance estimated on n - trace(L) degrees of freedom (L the smoothing operator), a close approximation to R’s t-interval construction.
Usage
stat-smooth(
method: "lm",
se: true,
level: 0.95,
span: 0.75,
degree: 2,
)Parameters
| Parameter | Default | Description |
|---|---|---|
method |
"lm" |
Smoother method: "lm" (weighted least squares line) or "loess" (tricube-weighted local polynomials). |
se |
true |
Whether to compute the confidence band. When false, ymin == ymax == y. |
level |
0.95 |
Confidence level for the band (e.g., 0.95). |
span |
0.75 |
Loess neighbourhood as a fraction of the data in (0, 1]; smaller spans follow the data more closely. |
degree |
2 |
Loess local polynomial degree: 0, 1, or 2. |
Returns
Statistic object with name: "smooth", consumed by geom layers.
Outputs
x.y.ymin.ymax.
Examples
Linear fit with the default 95% confidence band.
#let d = range(0, 20).map(i => (
x: i,
y: i * 0.5 + calc.sin(i * 0.4) * 2,
))
#plot(
data: d,
mapping: aes(x: "x", y: "y"),
layers: (
geom-point(size: 2pt),
geom-smooth(method: "lm"),
),
width: 10cm,
height: 6cm,
)
Constructor form: stat: stat-smooth() is equivalent to stat: "smooth" with defaults. Use the constructor on any geom and to customise method, se, or level. Both forms honour colour grouping.
#let d = ()
#for grp in ("a", "b") {
for i in range(0, 20) {
d.push((x: i, y: i * 0.5 + (if grp == "b" { 1.5 } else { 0 }) + calc.sin(i * 0.4), grp: grp))
}
}
#plot(
data: d,
mapping: aes(x: "x", y: "y", colour: "grp"),
layers: (
geom-point(size: 2pt),
geom-line(stat: stat-smooth(method: "lm", se: false)),
),
width: 10cm,
height: 6cm,
)
A loess curve follows the oscillation the linear fit averages away; span tunes how locally it bends.
#let d = range(0, 30).map(i => (
x: i * 0.4,
y: calc.sin(i * 0.4) * 2 + i * 0.1,
))
#plot(
data: d,
mapping: aes(x: "x", y: "y"),
layers: (
geom-point(size: 2pt),
geom-smooth(method: "loess", span: 0.5),
),
width: 10cm,
height: 6cm,
)
