mongodb

Question

{ "_id" : 0, "cityname" : "tallinn", "JAN" : -3 }

{ "_id" : 1, "cityname" : "beijing", "JAN" : -5 }

{ "_id" : 2, "cityname" : "berlin", "JAN" : 12 }

{ "_id" : 3, "cityname" : "buenose", "JAN" : 23 }

我想计算塔林到其他城市和北京到其他城市之间的距离它继续整个文档

这是我的java代码

try {
    BasicDBObject query = new BasicDBObject();
    BasicDBObject select = new BasicDBObject();
    select.put("JAN",1);
    select.put("_id",1);
    DBCursor cursor = coll.find(query,select);
    BasicDBObject obj = (BasicDBObject)cursor.next();
    int m,id;
    id=Integer.parseInt(obj.getString("_id"));
    for (int j=0;j<4;j++){
        m= Integer.parseInt(obj.getString("JAN"));
            if (id==j){
                while (cursor.hasNext()) {
                    int ma;
                    BasicDBObject object = (BasicDBObject)cursor.next();
                    ma= Integer.parseInt(object.getString("JAN"));
                    System.out.print((m-ma)+"  ");
                }
        }
    }
}
catch (MongoException e){
    System.out.println(e.getClass().getCanonicalName());
}

输出

 2 -9 -26

我期待这种类型的输出

0 2 -15 -26
-2 0 -17 -28
15 17 0 -11
26 28 11 0

Answer 1

首先，您应该找出所有不同的 cityname 并找到给定 city 的所有 JAN，然后遍历所有数据并减去该值。

检查下面的代码：

 Mongo mongo = new Mongo("localhost", 27017);
 DB db = mongo.getDB("dbName");
 DBCollection collection = db.getCollection("collectionName");
 List distinctCity = collection.distinct("cityname");
 for(int i = 0; i < distinctCity.size(); i++) {
   BasicDBObject query = new BasicDBObject();
   query.put("cityname", distinctCity.get(i));
   BasicDBObject project = new BasicDBObject();
   project.put("JAN", 1);
   project.put("_id", 0);
   DBCursor cursorDoc = collection.find(query, project);
   while(cursorDoc.hasNext()) {
     BasicDBObject object = (BasicDBObject) cursorDoc.next();
     Integer currentValue = object.getInt("JAN");
     DBCursor allData = collection.find(new BasicDBObject(), project);
     while(allData.hasNext()) {
       BasicDBObject allDataObject = (BasicDBObject) allData.next();
       Integer allDataJanValue = allDataObject.getInt("JAN");
       Integer result = currentValue - allDataJanValue;
       System.out.print("  " + result + "  ");
     }
     System.out.println();
   }
 }
 }

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