Formula Transform
The formula transform extends data objects with new values according to a calculation formula.
Transform Parameters
| Property | Type | Description |
|---|---|---|
| expr | Expr | Required. The formula expression for calculating derived values. |
| as | String | Required. The output field at which to write the formula value. |
| initonly | Boolean | If true, the formula is evaluated only when a data object is first observed. The formula values will not automatically update if data objects are modified. The default is false. |
Usage
{"type": "formula", "as": "logx", "expr": "log(datum.x) / LN10"}
This example computes the base-10 logarithm of x and stores the result as the logx field.
{"type": "formula", "as": "hr", "expr": "hours(datum.date)"}
This example extracts the hour of the date field, and stores the result as the hr field.