mongodb - How to run a .group() with Java -

i have query in mongodb , produces result want. i'm trying use in java.

this query in mongodb:

var red = function(doc, out) { out.count_order++; out.sum_qty += doc.quantity; out.sum_base_price += doc.extendedprice; out.sum_disc_price += doc.extendedprice * (1 - doc.discount); out.sum_charge += doc.extendedprice * (1 - doc.discount) * (1 + doc.tax); out.avg_disc += doc.discount; };  var avg = function(out) { out.avg_qty = out.sum_qty / out.count_order; out.avg_price = out.sum_base_price / out.count_order; out.avg_disc = out.avg_disc / out.count_order; };  db.lineitems.group( { key : { returnflag : true, linestatus : true}, cond : { "shipdate" : {$lte: 19980801}}, initial: { count_order : 0, sum_qty : 0, sum_base_price : 0, sum_disc_price : 0, sum_charge : 0, avg_disc : 0}, reduce : red, finalize : avg }); 

and way i'm using in java don't know how use avg function.

    string avg = "var avg = function(out) {"             + "out.avg_qty = out.sum_qty / out.count_order;"             + "out.avg_price = out.sum_base_price / out.count_order;"             + "out.avg_disc = out.avg_disc / out.count_order;};";      string reduce = "function(doc, out) {"             + "out.count_order++;"             + "out.sum_qty += doc.quantity;"             + "out.sum_base_price += doc.extendedprice;"             + "out.sum_disc_price += doc.extendedprice * (1 - doc.discount);"             + "out.sum_charge += doc.extendedprice * (1 - doc.discount) * (1 + doc.tax);"             + "out.avg_disc += doc.discount;};";      string finalize = "function(out) {"             + "out.avg_qty = out.sum_qty / out.count_order;"             + "out.avg_price = out.sum_base_price / out.count_order;"             + "out.avg_disc = out.avg_disc / out.count_order;};";      mapreduceiterable<document> iterable = collection.mapreduce(**????**, reduce).finalizefunction(finalize); 

how can use function?

you better off using aggreation framework calling .group() method, of course older implementation before aggregation framework existed.

the logic applied in shell be:

db.lineitems.aggregate([     { "$match": { "shipdate": { "$lte": 19980801 } },     { "$group": {         "_id": {             "returnflag": "$returnflag",             "linestatus": "$linestatus"         },         "count": { "$sum": 1 },         "sum_qty": { "$sum": "$quantity" },         "avg_qty": { "$avg": "$quantity" },         "sum_base_price": { "$sum": "$extendedprice" },         "avg_base_price": { "$avg": "$extendedprice" },         "sum_disc_price": {             "$sum": {                 "$multiply": [                     "$extendedprice",                     { "$subtract": [ 1, "$discount" ] }                 ]             }         },         "avg_disc_price": {             "$avg": {                 "$multiply": [                     "$extendedprice",                     { "$subtract": [ 1, "$discount" ] }                 ]             }         },         "sum_charge": {             "$sum": {                 "$multiply": [                     "$extendedprice",                     { "$subtract": [ 1, "$discount" ] },                     { "$add": [ 1, "$tax" ] }                 ]             }         },         "avg_disc": { "$avg": "$discount" }     }} ]) 

the aggregation framework efficient $group pipeline stage operator same things in native coded operations. there $sum , $avg accumulators built in other math operations.

in short, "natively coded" , not relying on "javascript interpretation", execution faster .group() can provide. plus should straightforward understand.

translating java like

list<document> pipeline = arrays.<document>aslist(   new document(     "$match", new document(       "shipdate", new document(         "$lte", 19980801                    )     )   ),   new document(     "$group", new document(       "_id", new document(         "returnflag", "$returnflag"       ).append( "linestatus", "$linestatus" )     ).append(       "count", new document( "$sum", 1 )     ).append(       "sum_qty", new document( "$sum", "$quantity" )     ).append(       "avg_qty", new document( "$avg", "$quantity" )     ).append(       "sum_base_price", new document( "$sum", "$extendedprice" )     ).append(       "avg_base_price", new document( "$avg", "$extendedprice" )     ).append(       "sum_disc_price", new document(         "$sum", new document(           "$multiply", arrays.aslist(             "$extendedprice",             new document(               "$subtract", arrays.aslist(1, "$discount")             )           )         )       )     ).append(       "avg_disc_price", new document(         "$avg", new document(           "$multiply", arrays.aslist(             "$extendedprice",             new document(               "$subtract", arrays.aslist(1, "$discount")             )           )         )       )     ).append(       "sum_charge", new document(         "$sum", new document(           "$multiply", arrays.aslist(             "$extendedprice",             new document(               "$subtract", arrays.aslist(1, "$discount")             ),             new document(               "$add", arrays.aslist(1, "$tax")             )           )         )       )     ).append(       "avg_disc", new document( "$avg", "$discount" )     )   ) );  aggregateiterable<document> result = collection.aggregate(pipeline);