Function Facet

docs/app/js/sanddance-app.js:117168–117178

* Facets a dataflow into a set of subflows based on a key. * @constructor * @param {object} params - The parameters for this operator. * @param {function(Dataflow, string): Operator} params.subflow - A function * that generates a subflow of operators and returns its root operator. * @param {f

(params)

 *   that generates a subflow of operators and returns its root operator.
 * @param {function(object): *} params.key - The key field to facet by.
 */ function Facet(params) {
    (0, _vegaDataflow.Transform).call(this, {}, params);
    this._keys = (0, _vegaUtil.fastmap)(); // cache previously calculated key values
    // keep track of active subflows, use as targets array for listeners
    // this allows us to limit propagation to only updated subflows
    const a = this._targets = [];
    a.active = 0;
    a.forEach = (f)=>{
        for(let i = 0, n = a.active; i < n; ++i)f(a[i], i, a);
    };
}
(0, _vegaUtil.inherits)(Facet, (0, _vegaDataflow.Transform), {
    activate (flow) {
        this._targets[this._targets.active++] = flow;