Mongo DB grouping datatype changes - mongodb

Question

I came across an odd occurrence while using mongodb + their java driver.
When I do a grouping query the datatype for the key changes from an int to a double.
(ie. I am grouping on a key for 'hours', which is stored as an int within all the objects, but the key changes into a double type in the results I get back).
It isn't a huge issue...but it is weird that it would just arbitrarily change the datatype of a key-value pair like that. Has anyone else had this come up? is this normal behaviour?
Thanks,
p.s. Doing a regular .find() query returns correct datatype, fyi.
Edit:
Some example code:
import com.mongodb.BasicDBObject;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.QueryOperators;
public class MongoTestQueries {
private static final String TESTDBNAME = "badgerbadgerbadger";
private static final String TESTCOLNAME = "mushroom";
private static final Long TESTMAX = 50L;
private static final String KEY1 = "a";
private static final String KEY2 = "snake";
private static final String KEY3 = "plane";
/**
* This starts running it.
*
* #param args
* the arguments.
*/
public static void main(final String[] args) {
//You'll need to write your own code here for connecting to db as you see fit.
MongoConnection mc = new MongoConnection("someserver.com", TESTDBNAME);
mc.setCurCol(TESTCOLNAME);
mc.getCurCol().drop();
mc.setCurCol(TESTCOLNAME);
DBCollection col = mc.getCurCol();
populateCollection(col);
System.out.println(col.count() + " inserted into db.");
regGroupSearch(col);
}
private static void populateCollection(DBCollection col) {
for (Long l = 0L; l < TESTMAX; l++) {
col.insert(new BasicDBObject(KEY1, new Integer(l.intValue())).append(KEY2,
Math.random()).append(KEY3, (TESTMAX - l) + "a string"));
}
}
private static void regGroupSearch(final DBCollection col) {
System.out.println("Group Search:");
DBObject key = new BasicDBObject(KEY1, true).append(KEY3, true);
DBObject cond = new BasicDBObject().append(KEY1, new BasicDBObject(QueryOperators.GT, 4.0));
DBObject initial = new BasicDBObject("count", 0).append("sum", 0);
String reduce = "function(obj,prev){prev.sum+=obj." + KEY2 + ",prev.count+=1}";
String finalize = "function(obj){obj.ave = obj.sum/obj.count}";
DBObject groupResult = col.group(key, cond, initial, reduce, finalize);
printDBObject(groupResult);
System.out.println("Done.");
}
private static void printDBObject(final DBObject toPrint) {
for (String k : toPrint.keySet()) {
System.out.println(k + ": " + toPrint.get(k));
}
}
}