RethinkDB group and merge into single doc with sub-array - mapreduce

Question

Is it the best way to group and merge each reduction into a single document with sub-array?
r.expr([
{id: 1, foo: 1, bar: 2, date: r.time(2016, 1, 1, 'Z')},
{id: 1, foo: 4, bar: 1, date: r.time(2016, 1, 3, 'Z')},
{id: 1, foo: 10, bar: 0, date: r.time(2016, 1, 2, 'Z')},
{id: 2, foo: 5, bar: 3, date: r.time(2016, 1, 1, 'Z')},
{id: 2, foo: 3, bar: 6, date: r.time(2016, 1, 2, 'Z')}
]).group('id').orderBy('date').map(function(d){
return d
.without('foo', 'bar', 'date')
.merge({stats: [d.pluck('foo', 'bar', 'date')]})
}).reduce(function(left, right){
return left .without('stats').merge({
stats: left('stats').append(right('stats')(0))
})
}).ungroup().map(function(g){
return g('reduction')
})
Output:
[
{
"id": 1 ,
"stats": [
{
"foo": 1, "bar": 2 , "date": Fri Jan 01 2016 00:00:00 GMT+00:00
},
{
"foo": 10, "bar": 0 , "date": Sat Jan 02 2016 00:00:00 GMT+00:00
} ,
{
"foo": 4, "bar": 1 , "date": Sun Jan 03 2016 00:00:00 GMT+00:00
}
]
},
{
"id": 2 ,
"stats": [
{
"foo": 5, "bar": 3, "date": Fri Jan 01 2016 00:00:00 GMT+00:00
} ,
{
"foo": 3, "bar": 6, "date": Sat Jan 02 2016 00:00:00 GMT+00:00
}
]
}
]

Answer 1

This should work:
r.expr([
{id: 1, foo: 1, bar: 2, date: r.time(2016, 1, 1, 'Z')},
{id: 1, foo: 4, bar: 1, date: r.time(2016, 1, 3, 'Z')},
{id: 1, foo: 10, bar: 0, date: r.time(2016, 1, 2, 'Z')},
{id: 2, foo: 5, bar: 3, date: r.time(2016, 1, 1, 'Z')},
{id: 2, foo: 3, bar: 6, date: r.time(2016, 1, 2, 'Z')}
]).group('id')
.orderBy('date')
.without('id')
.ungroup()
.map(rec => { return { id : rec('group'), stats : rec('reduction') }; } )