$group with $push
db.simple.aggregate( [ { $group: { _id: "$name", total: { $push : "$cnt" } } } ])
{
"result": [
{
"_id": "bar",
"total": [
5,
9
]
},
{
"_id": "foo",
"total": [
3,
4,
5
]
}
],
"ok": 1
}