zchking

//equivalent of MySQL SELECT COUNT(*) AS cnt, fieldName FROM someTable GROUP BY fieldName;
db.someCollection.aggregate([{"$group" : {_id:"$fieldName", cnt:{$sum:1}}}]);

//as above but ordered by the count descending
//eg: SELECT COUNT(*) AS cnt, fieldName FROM someTable GROUP BY fieldName ORDER BY cnt DESC;
db.someCollection.aggregate([{"$group" : {_id:"$fieldName", cnt:{$sum:1}}}, {$sort:{'cnt':-1}}]);

db.order.aggregate([{ $group: { _id: "$seller_email", total_order: { "$sum": 1 },
                              seller_address_1 : { $first: '$seller_address_1' },
                              seller_country : { $first: '$seller_country' },

zchking

Using numpy to build an array of all combinations of two arrays

Cartesian product function by Stackoverflow user, pv.

See Answer here.