let events = new EventEmitter();
let source = Rx.Observable.fromEvent( events, 'data' );

source
    .groupBy( event => event.type )
    .flatMap( group => group.reduce( ( acc, cur ) => _.merge( acc, cur ), [] ) )
    .subscribe( ( data ) => {
        console.log( data );
    } );


events.emit( 'data', { 'type': 1, msg: 'Test 1' } );
events.emit( 'data', { 'type': 1, msg: 'Test 2' } );
events.emit( 'data', { 'type': 2, msg: 'Test 3' } );