Statistics

A stat summarises a layer’s data before it’s drawn. Instead of plotting raw rows, the layer plots a computed result — a count, a mean, or a fitted regression line. Stats are set per layer through a geom’s stat option, and default to identity (draw the data as-is).

import { stat } from '@graphysdk/viz-engine';

geom.line({ stat: stat.smooth({ method: 'linear' }) });

Available stats

Stat	Result
`stat.identity()` (default)	The data unchanged
`stat.count()`	The number of observations per group
`stat.mean()`	The arithmetic mean per group
`stat.smooth({ method })`	A fitted regression curve through the points

Trendlines with `smooth`

The smooth stat fits a regression through a layer’s points — the basis for trendlines. Add it to a second geom.line() layer over your raw data:

pipe(
  createSpec({ x: 'date', y: 'sales' }),
  geom.point(), // the raw points
  geom.line({ stat: stat.smooth({ method: 'linear' }) }), // the trend
  scale.x(),
  scale.y()
);

method selects the regression family:

method

required

The regression method to fit.

order

number

Polynomial order — only used when method: 'polynomial'.

bandwidth

number

Smoothing bandwidth — only used when method: 'loess'.

stat.smooth({ method: 'polynomial', order: 4 });
stat.smooth({ method: 'loess', bandwidth: 0.5 });

A mean reference line

Pair stat.mean() with geom.rule() to draw a horizontal line at a series’ average:

pipe(
  createSpec({ x: 'month', y: 'revenue' }),
  geom.bar(),
  geom.rule({ stat: stat.mean() }), // a line at the mean revenue
  scale.x(),
  scale.y()
);

Transforms — reshape data before it reaches a stat
Geoms & layers — where the stat option lives

Get Started

Core concepts

Chart types

Annotations & emphasis

Rendering

Configuration

Advanced

Extending

Available stats

Trendlines with `smooth`

A mean reference line

Next

​Available stats

​Trendlines with smooth

​A mean reference line

​Next

Available stats

Trendlines with `smooth`

A mean reference line

Next