gistfile1.txt

in mongo shell, the following works:

db.getCollection('philly_seer').aggregate([
{ $match: {cause_code: 488}},
{ $group: {_id: "$date", total: {$sum: "$call_attempts"} } },
])


but in ruby, this will not work

match = { '$match' => {'cause_code' => 488}}
group = { '$group' => {'_id' => {$sum: "$call_attempts"} } }

coll.aggregate([match, group]) # returns an empty array.