Derived property functions

Functions can be used to create derived properties on objects. These can be displayed in the Selection panel and used to color objects on the map, as part of value-based styling.

Define a derived property function

Any function that takes in an array of objects and returns a FunctionsMap from object to a primitive can be used as a derived property. For example:

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import { Function, FunctionsMap, Double } from "@foundry/functions-api";
import { ExampleDataRoute } from "@foundry/ontology-api";

export class DerivedPropertyFunctions {
    @Function()
    public async flightCancellationPercentage(routes: ExampleDataRoute[]): Promise<FunctionsMap<ExampleDataRoute, Double>> {
        const routeMap = new FunctionsMap<ExampleDataRoute, Double>();

        const allFlights = await Promise.all(routes.map(route => route.flights.allAsync()));

        for (let i = 0; i < routes.length; i++) {
            const route = routes[i];
            const flights = allFlights[i];
            const cancelledFlights = flights.filter(flight => flight.cancelled);
            const cancellationPercentage = (cancelledFlights.length / flights.length) * 100;
            routeMap.set(route, cancellationPercentage);
        }

        return routeMap;
    }
}