Loess Transform
The loess transform ≥ 5.4 (for locally-estimated scatterplot smoothing) uses locally-estimated regression to produce a trend line. Loess performs a sequence of local weighted regressions over a sliding window of nearest-neighbor points. For standard parametric regression options, see the regression transform.
Transform Parameters
| Property | Type | Description |
|---|---|---|
| x | Field | Required. The data field for predictor (independent) values, typically associated with the x-axis. |
| y | Field | Required. The data field for predicted (dependent) values, typically associated with the y-axis. |
| groupby | Field[ ] | The data fields to group by. If not specified, a single group containing all data objects will be used. |
| bandwidth | Number | The bandwidth parameter for the loess method (default 0.3). |
| as | String | The output fields for the predictor and predicted values for the line of best fit. If unspecified, the x and y parameter field names will be used. |
Usage
Generate a loess trend line that models the field dv as a function of iv, using a bandwidth parameter of 0.2:
{
"type": "regression",
"method": "loess",
"x": "dv",
"y": "iv",
"bandwidth": 0.2
}
Generates a new data stream with points for a trend line that can then be visualized with a line mark.