/**
* Performs {@link https://en.wikipedia.org/wiki/Cartesian_product | cross-product} between two
* {@link /muze/docs/api-datamodel | DataModel} instances with an optional predicate which determines which tuples
* should be included and returns a new {@link /muze/docs/api-datamodel | DataModel} instance containing the results.
* This operation is also called theta join.
*
* Cross product takes two set and create one set where each value of one set is paired with each value of another
* set.
*
* This method takes an optional predicate which filters the generated result rows. The predicate is called for
* every tuple. If the predicate returns true the combined row is included in the resulatant table.
*
* @example
* //@preamble_start
* Promise.all([loadData('/static/cars.json'), loadData('/static/cars-schema.json')]).then(function (params) {
* const data = params[0];
* const schema = params[1];
* const DataModel = muze.DataModel;
* const dm = new DataModel(data, schema);
* //@preamble_end
* // DataModel instance is created from https://www.charts.com/static/cars.json data,
* // https://www.charts.com/static/cars-schema.json schema and assigned to variable dm. DataModel is extracted from
* // muze namespace and assigned to the variable DataModel.
*
* // Creates two small DataModel instance from the original DataModel instance, which will be joined.
* let makerDM = dm.groupBy(['Origin', 'Maker']).project(['Origin', 'Maker']);
* let nameDM = dm.project(['Name','Miles_per_Gallon']);
*
* const join = DataModel.Operators.join;
* let outputDM = join(makerDM, nameDM,
* (makerDM, nameDM) => makerDM.Maker.value === nameDM.Name.value.split(/\s/)[0]);
* //@preamble_start
* printDM(outputDM);
* });
* //@preamble_end
*
* @public
* @segment Operators
*
* @param {DataModel} leftDM Instance of DataModel
* @param {DataModel} rightDM Instance of DataModel
* @param {SelectionPredicate} filterFn - The predicate function that will filter the result of the crossProduct.
*
* @return {DataModel} New DataModel instance created after joining.
*/
export function join () { /* @warn pseudo function to mock documentation */ }