Error in MapReduce command with MongoDB Java API

Question

I'm testing the MongoDB Java API and I wanted to do a mapReduce. I implemented it as follow :

String map = "function() { " +
    "emit(this.ts, this.1_bid);}";

String reduce = "function(key, values) {" +
    "return Array.sum(values);}";

MapReduceCommand cmd = new MapReduceCommand(collection, map, reduce, null, MapReduceCommand.OutputType.INLINE, null);
MapReduceOutput out = collection.mapReduce(cmd);

for (DBObject o : out.results()) {
    System.out.println(o.toString());
}

But when I execute it I have the following exception stack :

[tick_engine] 16:51:53.600 ERROR [MongoTickDataReader] Failed to read data from mongoDB
com.mongodb.CommandFailureException: { "serverUsed" : "/127.0.0.1:27017" , "errmsg" : "exception: SyntaxError: Unexpected token ILLEGAL" , "code" : 16722 , "ok" : 0.0}
    at com.mongodb.CommandResult.getException(CommandResult.java:71) ~[mongo-2.11.1.jar:na]
    at com.mongodb.CommandResult.throwOnError(CommandResult.java:110) ~[mongo-2.11.1.jar:na]
    at com.mongodb.DBCollection.mapReduce(DBCollection.java:1265) ~[mongo-2.11.1.jar:na]
    at com.smarttrade.tickEngine.in.MongoTickDataReader.mapReduce(MongoTickDataReader.java:321) ~[classes/:na]
    at com.smarttrade.tickEngine.in.MongoTickDataReader.readData(MongoTickDataReader.java:157) ~[classes/:na]
    at com.smarttrade.tick.engine.TickEngine.onMarketDataRequest(TickEngine.java:203) [classes/:na]
    at com.smarttrade.tick.sttp.TickMarketDataRequestCommand.execute(TickMarketDataRequestCommand.java:62) [classes/:na]
    at com.smarttrade.st.commands.Command.process(Command.java:140) [src/:na]
    at com.smarttrade.st.server.STTPInvoker$1.process(STTPInvoker.java:385) [src/:na]
    at com.smarttrade.st.server.STTPInvoker$1.process(STTPInvoker.java:1) [src/:na]
    at com.smarttrade.util.concurrent.queue.MultiSessionsBlockingQueue$SimpleSession.run(MultiSessionsBlockingQueue.java:122) [src/:na]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_51]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_51]
    at java.lang.Thread.run(Thread.java:744) [na:1.7.0_51]

hellboy · Accepted Answer · 2014-04-04 19:05:17Z

The problem seems to be with the attribute name that you have defined - 1_bid

I created sample documents to test your map-reduce -

{ "_id" : ObjectId("533ef7d0e1687dd644410d88"), "ts" : "TSKEY", "1_bid" : 200 }
{ "_id" : ObjectId("533ef7d3e1687dd644410d89"), "ts" : "TSKEY", "1_bid" : 300 }
{ "_id" : ObjectId("533ef7d5e1687dd644410d8a"), "ts" : "TSKEY", "1_bid" : 400 }
{ "_id" : ObjectId("533ef7dce1687dd644410d8b"), "ts" : "TSKEY2", "1_bid" : 800 }
{ "_id" : ObjectId("533ef7dfe1687dd644410d8c"), "ts" : "TSKEY2", "1_bid" : 300 }

I ran following map-reduce command -

db.sample4.mapReduce(function() { emit(this.ts, this.1_bid);},function(key, values) {return Array.sum(values);})

The error that I got is SyntaxError: missing ) after argument list (shell):1

I realized, that the function, that mapper is executing, is a JavaScript function and in Javascript, you cannot have a variable that starts with a number. Hence you get a syntax error. I then created new set of documents -

{ "_id" : ObjectId("533eff29e1687dd644410d8d"), "ts" : "TSKEY", "bid_1" : 200 }
{ "_id" : ObjectId("533eff2de1687dd644410d8e"), "ts" : "TSKEY", "bid_1" : 300 }
{ "_id" : ObjectId("533eff34e1687dd644410d8f"), "ts" : "TSKEY", "bid_1" : 400 }
{ "_id" : ObjectId("533eff7fe1687dd644410d92"), "ts" : "TSKEY2", "bid_1" : 800 }
{ "_id" : ObjectId("533eff85e1687dd644410d93"), "ts" : "TSKEY2", "bid_1" : 300 }

and then modified the mapper to use "bid_1" and ran the following command -

db.sample4.mapReduce(function() { emit(this.ts, this.bid_1);},function(key, values) {return Array.sum(values);},"pivot")

The output was - { "result" : "pivot", "timeMillis" : 61, "counts" : { "input" : 12, "emit" : 12, "reduce" : 2, "output" : 2 }, "ok" : 1, }

db.pivot.find()
{ "_id" : "TSKEY", "value" : 900 }
{ "_id" : "TSKEY2", "value" : 1100 }

I tested this in Java using the same program that you have pasted and just changed the attribute name to "bid_1" and it worked

Makimura · Accepted Answer · 2015-05-18 09:18:45Z

0

To prevent syntax errors on field names, you can also write the map function this way :

function() {
  emit(this["ts"], this["1_bid"]);
}

answered May 18, 2015 at 9:18

Makimura

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