map reduce function to count the documents- mongodb - mongodb

Question

I have a Collection with the following fields:
TestTable
{
"ID"
"Name"
"Ver"
"Serial"
"DateTime"
"FeatureID"
"FeatureName"
}
I want to have a map reduce function to get the count of the records in a particular Year.
The map reduce function i wrote is:
map= function(){
year= Date.UTC(this.DateTime.getFullYear());
emit({year: year}, {count: 1});
}
reduce= function(key, values){
var count=0;
for(v in values){
count+= v['count'];
});
return {count: count};
}
Now the output should give the count of douments in each year. Is the map reduce function correct?
The result i got is:
> db.Years.find()
{ "_id" : { "year" : NaN }, "value" : { "count" : NaN } }
> db.Years.find().count()
1
Which is not what i expected.
edited
one of the TestTable document:
> db.TestTable.findOne()
{
"_id" : ObjectId("527c48e99000cf10bc2a1d82"),
"ID" : "LogID16587",
"Name" : "LogName15247",
"Ver" : "VersionID11",
"Serial" : "ProductID727",
"DateTime" : ISODate("1998-12-15T18:30:00Z"),
"FeatureID" : "FeatureID465",
"FeatureName" : "FeatureName 1460"
}
Thanks in advance.

Answer 1

Date.UTC requires both year and month parameters. So your map function should look like this instead:
map= function(){
year= Date.UTC(this.DateTime.getFullYear(), 0);
emit({year: year}, {count: 1});
}
Also, don't use in to iterate over the elements of an array in your reduce method as it doesn't work in the way you're using it. Use a traditional for loop instead:
reduce= function(key, values){
var count=0;
for(var i=0; i<values.length; i++) {
count += values[i]['count'];
};
return {count: count};
}