MJSplot_author

    conv = c.aggregate({
       "a": c.reduce(c.ReduceFuncs.Array, c.item("a")),
       "a_sum": c.reduce(c.ReduceFuncs.Sum, c.item("a")),
       "b": c.reduce(c.ReduceFuncs.ArrayDistinct, c.item("b")),
    }).gen_converter()
    conv(input_data)

    conv = lambda data:{ 'a': [el['a'] for el in data ],
                    'a_sum' : sum( [el['a'] for el in data ]),
                    'b': list(set( [el['b'] for el in data ])), }
    conv(input_data) 

    let a = {key: 'a'};
    
    function foo( a ) {
      a['otherKey'] = 'b';
    }
    
    foo( a );
    
    console.log( a ); // {key: 'a',otherKey: 'b'}