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Problem with MapReduce

I have a strange MapReduce problem.

Card Function:

> mp function () { emit(this.ContractID, {qty:this.Qty, qtybs:this.QtyBs}); }

Decrease function

 > red function (key, values) { var sum1 = 0, sum2 = 0; values.forEach(function (doc) {sum1 += doc.qty;sum2 += doc.qtybs;}); return {a:sum1, b:sum2}; }

Launch MR for 7 contracts:

 > result = db.fact_payments.mapReduce(mp, red, {out:"myout2", query:{ContractID:{$lte:10000100042}}}); { "result" : "myout2", "timeMillis" : 670, "counts" : { "input" : 591, "emit" : 591, "output" : 7 }, "ok" : 1, } > db.myout2.find() { "_id" : NumberLong("10000000042"), "value" : { "a" : 8331.04, "b" : 253835.07999999996 } } { "_id" : NumberLong("10000000084"), "value" : { "a" : 4728.480000000001, "b" : 142879.88000000003 } } { "_id" : NumberLong("10000000129"), "value" : { "a" : 25421.859999999997, "b" : 756036.9499999998 } } { "_id" : NumberLong("10000000140"), "value" : { "a" : 477292.0000000002, "b" : 477292.0000000002 } } { "_id" : NumberLong("10000000148"), "value" : { "a" : 7912.0599999999995, "b" : 237926.87999999998 } } { "_id" : NumberLong("10000000165"), "value" : { "a" : 35391.31999999999, "b" : 1074180.95 } } { "_id" : NumberLong("10000000171"), "value" : { "a" : 62189.52, "b" : 62189.52 } } >

Everything is in order, all contracts have results :)

Run MR for all contracts:

 > result = db.fact_payments.mapReduce(mp, red, {out:"myout2", query:{ContractID:{$lte:100100000042}}}); { "result" : "myout2", "timeMillis" : 26273, "counts" : { "input" : 295765, "emit" : 295765, "output" : 7793 }, "ok" : 1, } > db.myout2.find() { "_id" : NumberLong("10000000042"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10000000084"), "value" : { "a" : 4728.480000000001, "b" : 142879.88000000003 } } { "_id" : NumberLong("10000000129"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10000000140"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10000000148"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10000000165"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10000000171"), "value" : { "a" : 62189.52, "b" : 62189.52 } } { "_id" : NumberLong("10005000172"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10005000173"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10005000189"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10005000191"), "value" : { "a" : 8261.759999999998, "b" : 253916.7 } } { "_id" : NumberLong("10005000199"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10005000206"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10005000213"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10010000200"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10010000224"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10010000229"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10010000240"), "value" : { "a" : 32843.32, "b" : 32843.32 } } { "_id" : NumberLong("10010000243"), "value" : { "a" : NaN, "b" : NaN } } { "_id" : NumberLong("10010000244"), "value" : { "a" : NaN, "b" : NaN } } has more

The same contract identifier with different results:

 { "_id" : NumberLong("10000000042"), "value" : { "a" : 8331.04, "b" : 253835.07999999996 } }

and

 { "_id" : NumberLong("10000000042"), "value" : { "a" : NaN, "b" : NaN } }

I have no ideas.

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1 answer

If you change the last line to the next, it should work:

 return {qty:sum1, qtybs:sum2};

The rule is that the return value of the reduction function must be the same "shape" than the second argument to emit (which is the input being reduced), since the output of the reduction is returned back to the reduction function. See http://www.mongodb.org/display/DOCS/MapReduce#MapReduce-ReduceFunction for more details.

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