code: function AggregateByKey(sc, dependencies, reducer, combiner, init, args) {
    Dataset.call(this, sc, dependencies);
    this.combiner = combiner;
    this.reducer = reducer;
    this.init = init;
    this.args = args;
    this.shuffling = true;
    this.executed = false;
    this.buffer = {};
    this.type = 'AggregateByKey';
  }
docs: AggregateByKey is the main [k,v] transform on top of which all others [k,v] transforms are implemented.