OnlineLowess API

See also: fastLowess

When to Use

• Data arrives incrementally (sensors, streams)
• Need real-time smoothed values
• Fixed memory budget

Class

OnlineLowess

The OnlineLowess class updates the model incrementally with new data points.

Constructor:

const { OnlineLowess } = require('fastlowess-wasm');

const online = new OnlineLowess({ fraction: 0.5 }, { window_capacity: 50, min_points: 3 });
console.log("typeof add_point:", typeof online.add_point);

typeof add_point: function

• options: An object containing LowessOptions fields.
• onlineOptions: An object containing OnlineOptions fields.

Methods:

const { OnlineLowess } = require('fastlowess-wasm');

const n = 100;
const x = Float64Array.from({ length: n }, (_, i) => i * 2 * Math.PI / (n - 1));
const y = Float64Array.from(x, xi => Math.sin(xi) + 0.1);

const online = new OnlineLowess({ fraction: 0.5 }, { window_capacity: 50, min_points: 3 });

// Returns null until min_points (3) are reached
online.add_point(x[0], y[0]);  // null
online.add_point(x[1], y[1]);  // null

// Returns OnlineOutput once enough points are available
const result = online.add_point(x[2], y[2]);
console.log("Smoothed y:", result.y);

Smoothed y: 0.22659245357374927

• Adds a single point to the sliding window. Returns an OnlineOutput once enough points are available, or null while the window is still filling.

Options Structure

OnlineOptions (inherits LowessOptions)

Field	Type	Default	Description
window_capacity	number	1000	Max points in sliding window
min_points	number	2	Min points before smoothing starts
update_mode	string	"incremental"	Update mode ("full" or "incremental")
parallel	boolean	false	Enable parallel execution (off by default; online LOWESS fits one point at a time)

Result Structure

OnlineOutput

Returned by add_point() once the window has enough points (null until then).

Field	Type	Description
y	number	Smoothed value for the latest point
standard_error	number | undefined	Standard error (if requested)
residual	number | undefined	Residual y − smoothed (if requested)
robustness_weight	number | undefined	Robustness weight (if requested)
iterations_used	number | undefined	Robustness iterations performed

Options

update_mode

See: Execution Modes

Mode	Alias	Behavior	Speed
"incremental" (default)	"single"	Update only affected fits	Faster
"full"	"resmooth"	Recompute entire window	More accurate