MongoDB - 计算每日（日间）差异

【问题标题】：MongoDB - Calculate daily (inter-day) differenceMongoDB - 计算每日（日间）差异
【发布时间】：2016-04-03 18:51:07
【问题描述】：

这就是我的原始数据的样子。基本上它是一个每天都会更新数量的库存，因此具有相同名称的字段是指相同的项目类别但在不同的时间点：

{
    "_id" : ObjectId("56828a929da4bc16eb534ea4"), 
    "name" : "Laser Sable", 
    "datetime" : ISODate("2015-12-29T13:28:50.823+0000"),
    "units": 10,
    "price": 100
}, 
{
    "_id" : ObjectId("56828a929da4bc16eb534ea5"), 
    "name" : "Flying Skateboard", 
    "datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
    "units": 3,
    "price": 50
},
{
    "_id" : ObjectId("56828a929da4bc16eb534ea6"), 
    "name" : "Laser Sable", 
    "datetime" : ISODate("2015-12-28T13:28:50.823+0000"),
    "units": 7
    "price": 100
}, 
{
    "_id" : ObjectId("56828a929da4bc16eb534ea7"), 
    "name" : "Flying Skateboard", 
    "datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
    "units": 1,
    "price": 50
}

做了aggregation $group查询后，我有一组这样的数据

{
    "_id" : {
        "day" : NumberInt(29), 
        "month" : NumberInt(12), 
        "year" : NumberInt(2015)
    }, 
    "things" : [
        {
            "_id" : ObjectId("56828a929da4bc16eb534ea4"), 
            "name" : "Laser Sable", 
            "datetime" : ISODate("2015-12-29T13:28:50.823+0000"),
            "units": 10
        }, 
        {
            "_id" : ObjectId("56828a929da4bc16eb534ea5"), 
            "name" : "Flying Skateboard", 
            "datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
            "units": 3
        }
    ]
},
{
    "_id" : {
        "day" : NumberInt(28), 
        "month" : NumberInt(12), 
        "year" : NumberInt(2015)
    }, 
    "things" : [
        {
            "_id" : ObjectId("56828a929da4bc16eb534ea6"), 
            "name" : "Laser Sable", 
            "datetime" : ISODate("2015-12-28T13:28:50.823+0000"),
            "units": 7
        }, 
        {
            "_id" : ObjectId("56828a929da4bc16eb534ea7"), 
            "name" : "Flying Skateboard", 
            "datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
            "units": 1
        }
    ]
}

我根据获取数据的日期对项目进行了分组。我想有一种方法来计算每个项目的每日差异。这将意味着有一个新的字段“差异”，它将从昨天的单位中减去当前单位。我一直试图在aggregation framework 中实现这一点，但我正在努力寻找引用 f.ex 的方法：“名称相同且日期相同时的单位 -1”提前致谢！

编辑：

预期的输出是这样的：

{
"_id" : {
    "day" : NumberInt(29), 
    "month" : NumberInt(12), 
    "year" : NumberInt(2015)
}, 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea4"), 
        "name" : "Laser Sable", 
        "datetime" : ISODate("2015-12-29T13:28:50.823+0000"),
        "units": 10,
        "daily difference":3
    }, 
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea5"), 
        "name" : "Flying Skateboard", 
        "datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
        "units": 3,
        "daily difference":2
    }
]
}

【问题讨论】：

  • 你能发布你的预期输出吗？如果您正在尝试做我认为您正在尝试做的事情，那么在单个查询中是不可能的。
  • 我刚刚编辑了问题以提供预期的输出。我想要的是每天跟踪库存差异，所以我想计算每天的每日差异，然后对“每日差异”进行总结。

标签： mongodb mongodb-query aggregation-framework


【解决方案1】：

最后我只用了一个聚合查询就做到了，但是有 6 个步骤，它可能不是最优化的方法，但它确实有效。我的小怪兽来了：

db.stuff.aggregate(

// Pipeline
[
// Stage 1
{
  $project: { 
      "_id" : 1, 
      "units" : 1, 
      "price" : 1, 
      "name" : 1, 
      "dayyear" : [
          {
              "$dayOfYear" : "$datetime"
          }, 
          {
              "$multiply" : [
                  {
                      "$add" : [
                          {
                              "$dayOfYear" : "$datetime"
                          }, 
                          1
                      ]
                  }, 
                  -1
              ]
          }
      ], 
      "datetime" : 1
  }
},

// Stage 2
{
  $unwind: "$dayyear"
},

// Stage 3
{
  $project: { 
      "_id" : 1, 
      "difference" : {
          "$multiply" : [
              {
                  "$cond" : {
                      "if" : {
                          "$lt" : [
                              "$dayyear", 
                              0
                          ]
                      }, 
                      "then" : 1, 
                      "else" : -1
                  }
              }, 
              "$units"
          ]
      }, 
      "units" : {
          "$multiply" : [
              {
                  "$cond" : {
                      "if" : {
                          "$lt" : [
                              "$dayyear", 
                              0
                          ]
                      }, 
                      "then" : 1, 
                      "else" : -1
                  }
              }, 
              "$units"
          ]
      }, 
      "price" : {
          "$multiply" : [
              {
                  "$cond" : {
                      "if" : {
                          "$lt" : [
                              "$dayyear", 
                              0
                          ]
                      }, 
                      "then" : 1, 
                      "else" : -1
                  }
              }, 
              "$price"
          ]
      }, 
      "price difference" : {
          "$multiply" : [
              {
                  "$cond" : {
                      "if" : {
                          "$lt" : [
                              "$dayyear", 
                              0
                          ]
                      }, 
                      "then" : -1, 
                      "else" : 1
                  }
              }, 
              "$price"
          ]
      }, 
      "name" : 1, 
      "dayyear" : {
          "$cond" : {
              "if" : {
                  "$eq" : [
                      {
                          "$abs" : "$dayyear"
                      }, 
                      366
                  ]
              }, 
              "then" : 1, 
              "else" : {
                  "$abs" : "$dayyear"
              }
          }
      }, 
      "year" : {
          "$cond" : {
              "if" : {
                  "$eq" : [
                      {
                          "$abs" : "$dayyear"
                      }, 
                      366
                  ]
              }, 
              "then" : {
                  "$add" : [
                      {
                          "$year" : "$datetime"
                      }, 
                      1
                  ]
              }, 
              "else" : {
                  "$year" : "$datetime"
              }
          }
      }, 
      "datetime" : 1
  }
},

// Stage 4
{
  $group: { 
      "_id" : {
          "dayyear" : "$dayyear", 
          "year" : "$year", 
          "name" : "$name"
      }, 
      "difference" : {
          "$push" : "$difference"
      }, 
      "price difference" : {
          "$push" : "$price difference"
      }, 
      "things" : {
          "$push" : "$$ROOT"
      }
  }
},


// Stage 5
{
  $project: { 
      "_id" : {
          "$arrayElemAt" : [
              "$things._id", 
              0
          ]
      }, 
      "dayyear" : "$_id.dayyear", 
      "year" : "$_id.year", 
      "name" : "$_id.name", 
      "datetime" : "$things.datetime", 
      "difference" : {
          "$cond" : {
              "if" : {
                  "$eq" : [
                      {
                          "$size" : [
                              "$difference"
                          ]
                      }, 
                      2
                  ]
              }, 
              "then" : {
                  "$add" : [
                      {
                          "$arrayElemAt" : [
                              "$difference", 
                              0
                          ]
                      }, 
                      {
                          "$arrayElemAt" : [
                              "$difference", 
                              1
                          ]
                      }
                  ]
              }, 
              "else" : 0
          }
      }, 
      "price difference" : {
          "$cond" : {
              "if" : {
                  "$eq" : [
                      {
                          "$size" : [
                              "$price difference"
                          ]
                      }, 
                      2
                  ]
              }, 
              "then" : {
                  "$add" : [
                      {
                          "$arrayElemAt" : [
                              "$price difference", 
                              0
                          ]
                      }, 
                      {
                          "$arrayElemAt" : [
                              "$price difference", 
                              1
                          ]
                      }
                  ]
              }, 
              "else" : 0
          }
      }, 
      "units" : {
          "$cond" : {
              "if" : {
                  "$lt" : [
                      {
                          "$arrayElemAt" : [
                              "$things.units", 
                              0
                          ]
                      }, 
                      0
                  ]
              }, 
              "then" : {
                  "$abs" : {
                      "$arrayElemAt" : [
                          "$things.units", 
                          0
                      ]
                  }
              }, 
              "else" : {
                  "$abs" : {
                      "$arrayElemAt" : [
                          "$things.units", 
                          1
                      ]
                  }
              }
          }
      }, 
      "price" : {
          "$cond" : {
              "if" : {
                  "$lt" : [
                      {
                          "$arrayElemAt" : [
                              "$things.price", 
                              0
                          ]
                      }, 
                      0
                  ]
              }, 
              "then" : {
                  "$abs" : {
                      "$arrayElemAt" : [
                          "$things.price", 
                          0
                      ]
                  }
              }, 
              "else" : {
                  "$abs" : {
                      "$arrayElemAt" : [
                          "$things.price", 
                          1
                      ]
                  }
              }
          }
      }
  }
},

// Stage 6
{
  $project: { 
      "_id" : 1, 
      "name" : 1, 
      "units" : 1, 
      "price" : 1, 
      "dayyear" : 1, 
      "year" : 1, 
      "datetime" : {
          "$ifNull" : [
              {
                  "$cond" : {
                      "if" : {
                          "$eq" : [
                              {
                                  "$dayOfYear" : {
                                      "$arrayElemAt" : [
                                          "$datetime", 
                                          0
                                      ]
                                  }
                              }, 
                              "$dayyear"
                          ]
                      }, 
                      "then" : {
                          "$arrayElemAt" : [
                              "$datetime", 
                              0
                          ]
                      }, 
                      "else" : {
                          "$arrayElemAt" : [
                              "$datetime", 
                              1
                          ]
                      }
                  }
              }, 
              {
                  "$add" : [
                      {
                          "$arrayElemAt" : [
                              "$datetime", 
                              0
                          ]
                      }, 
                      86400000
                  ]
              }
          ]
      }, 
      "difference" : 1, 
      "total difference" : {
          "$multiply" : [
              "$price", 
              "$difference"
          ]
      }, 
      "price difference" : 1, 
      "inventory adjust for price change" : {
          "$multiply" : [
              "$price difference", 
              "$units"
          ]
      }, 
      "unitsprice" : {
          "$multiply" : [
              "$price", 
              "$units"
          ]
      }
  }
},
]
);

基本上我所做的是：

第 1 阶段：我将 day 字段更改为数组，作为第一个元素 该字段的原始日期，第二个，（原始日期+1） 乘以-1。我乘它的原因是为了能够 稍后将“克隆”与原件区分开来。

{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
"units" : NumberInt(10), 
"price" : NumberInt(100), 
"dayyear" : [
    NumberInt(363), 
    NumberInt(-364)
    ]
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
"units" : NumberInt(3), 
"price" : NumberInt(50), 
"dayyear" : [
    NumberInt(363), 
    NumberInt(-364)
    ]
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea6"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
"units" : NumberInt(7), 
"price" : NumberInt(100), 
"dayyear" : [
    NumberInt(362), 
    NumberInt(-363)
    ]
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea7"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
"units" : NumberInt(1), 
"price" : NumberInt(50), 
"dayyear" : [
    NumberInt(362), 
    NumberInt(-363)
    ]
}

第 2 阶段：我使用 day 变量展开，所以现在每个输入都是 重复（请注意，所有克隆都被“标记”，因为它们的日期在 负）。

{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
"units" : NumberInt(10), 
"price" : NumberInt(100), 
"dayyear" : NumberInt(363)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
"units" : NumberInt(10), 
"price" : NumberInt(100), 
"dayyear" : NumberInt(-364)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
"units" : NumberInt(3), 
"price" : NumberInt(50), 
"dayyear" : NumberInt(363)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
"units" : NumberInt(3), 
"price" : NumberInt(50), 
"dayyear" : NumberInt(-364)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea6"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
"units" : NumberInt(7), 
"price" : NumberInt(100), 
"dayyear" : NumberInt(362)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea6"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
"units" : NumberInt(7), 
"price" : NumberInt(100), 
"dayyear" : NumberInt(-363)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea7"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
"units" : NumberInt(1), 
"price" : NumberInt(50), 
"dayyear" : NumberInt(362)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea7"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
"units" : NumberInt(1), 
"price" : NumberInt(50), 
"dayyear" : NumberInt(-363)
}

第 3 阶段：在这里我结合了两个动作。首先，我将“原始”中的单位和价格（在“dayyear”中具有正数的那些）乘以 -1，然后将克隆中的差异乘以 -1（在这里你也可以做相反的事情 -将原始差异而不是克隆差异乘以 -1，这将取决于您希望如何计算差异）然后还将所有天数转换为正数（以便之后能够按该字段分组）。此外，如果我在一年的最后一天进行库存，我会设置条件，以便克隆指的是次年的第一年。

{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
"units" : NumberInt(-10), 
"price" : NumberInt(-100), 
"dayyear" : NumberInt(363), 
"difference" : NumberInt(-10), 
"price difference" : NumberInt(100), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
"units" : NumberInt(10), 
"price" : NumberInt(100), 
"dayyear" : NumberInt(364), 
"difference" : NumberInt(10), 
"price difference" : NumberInt(-100), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
"units" : NumberInt(-3), 
"price" : NumberInt(-50), 
"dayyear" : NumberInt(363), 
"difference" : NumberInt(-3), 
"price difference" : NumberInt(50), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
"units" : NumberInt(3), 
"price" : NumberInt(50), 
"dayyear" : NumberInt(364), 
"difference" : NumberInt(3), 
"price difference" : NumberInt(-50), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea6"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
"units" : NumberInt(-7), 
"price" : NumberInt(-100), 
"dayyear" : NumberInt(362), 
"difference" : NumberInt(-7), 
"price difference" : NumberInt(100), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea6"), 
"name" : "Laser Sable", 
"datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
"units" : NumberInt(7), 
"price" : NumberInt(100), 
"dayyear" : NumberInt(363), 
"difference" : NumberInt(7), 
"price difference" : NumberInt(-100), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea7"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
"units" : NumberInt(-1), 
"price" : NumberInt(-50), 
"dayyear" : NumberInt(362), 
"difference" : NumberInt(-1), 
"price difference" : NumberInt(50), 
"year" : NumberInt(2015)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea7"), 
"name" : "Flying Skateboard", 
"datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
"units" : NumberInt(1), 
"price" : NumberInt(50), 
"dayyear" : NumberInt(363), 
"difference" : NumberInt(1), 
"price difference" : NumberInt(-50), 
"year" : NumberInt(2015)
}

第 4 阶段：在这里我按名称、年份和日期分组，所以现在我有一个数组 做价格差异，另一个做单位差异

{ 
"_id" : {
    "dayyear" : NumberInt(362), 
    "year" : NumberInt(2015), 
    "name" : "Flying Skateboard"
}, 
"difference" : [
    NumberInt(-1)
], 
"price difference" : [
    NumberInt(50)
], 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea7"), 
        "name" : "Flying Skateboard", 
        "datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
        "units" : NumberInt(-1), 
        "price" : NumberInt(-50), 
        "dayyear" : NumberInt(362), 
        "difference" : NumberInt(-1), 
        "price difference" : NumberInt(50), 
        "year" : NumberInt(2015)
    }
]
}
{ 
"_id" : {
    "dayyear" : NumberInt(362), 
    "year" : NumberInt(2015), 
    "name" : "Laser Sable"
}, 
"difference" : [
    NumberInt(-7)
], 
"price difference" : [
    NumberInt(100)
], 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea6"), 
        "name" : "Laser Sable", 
        "datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
        "units" : NumberInt(-7), 
        "price" : NumberInt(-100), 
        "dayyear" : NumberInt(362), 
        "difference" : NumberInt(-7), 
        "price difference" : NumberInt(100), 
        "year" : NumberInt(2015)
    }
]
}
{ 
"_id" : {
    "dayyear" : NumberInt(363), 
    "year" : NumberInt(2015), 
    "name" : "Flying Skateboard"
}, 
"difference" : [
    NumberInt(-3), 
    NumberInt(1)
], 
"price difference" : [
    NumberInt(50), 
    NumberInt(-50)
], 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea5"), 
        "name" : "Flying Skateboard", 
        "datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
        "units" : NumberInt(-3), 
        "price" : NumberInt(-50), 
        "dayyear" : NumberInt(363), 
        "difference" : NumberInt(-3), 
        "price difference" : NumberInt(50), 
        "year" : NumberInt(2015)
    }, 
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea7"), 
        "name" : "Flying Skateboard", 
        "datetime" : ISODate("2015-12-28T13:28:50.912+0000"), 
        "units" : NumberInt(1), 
        "price" : NumberInt(50), 
        "dayyear" : NumberInt(363), 
        "difference" : NumberInt(1), 
        "price difference" : NumberInt(-50), 
        "year" : NumberInt(2015)
    }
]
}
{ 
"_id" : {
    "dayyear" : NumberInt(364), 
    "year" : NumberInt(2015), 
    "name" : "Laser Sable"
}, 
"difference" : [
    NumberInt(10)
], 
"price difference" : [
    NumberInt(-100)
], 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea4"), 
        "name" : "Laser Sable", 
        "datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
        "units" : NumberInt(10), 
        "price" : NumberInt(100), 
        "dayyear" : NumberInt(364), 
        "difference" : NumberInt(10), 
        "price difference" : NumberInt(-100), 
        "year" : NumberInt(2015)
    }
]
}
{ 
"_id" : {
    "dayyear" : NumberInt(364), 
    "year" : NumberInt(2015), 
    "name" : "Flying Skateboard"
}, 
"difference" : [
    NumberInt(3)
], 
"price difference" : [
    NumberInt(-50)
], 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea5"), 
        "name" : "Flying Skateboard", 
        "datetime" : ISODate("2015-12-29T13:28:50.912+0000"), 
        "units" : NumberInt(3), 
        "price" : NumberInt(50), 
        "dayyear" : NumberInt(364), 
        "difference" : NumberInt(3), 
        "price difference" : NumberInt(-50), 
        "year" : NumberInt(2015)
    }
]
}
{ 
"_id" : {
    "dayyear" : NumberInt(363), 
    "year" : NumberInt(2015), 
    "name" : "Laser Sable"
}, 
"difference" : [
    NumberInt(-10), 
    NumberInt(7)
], 
"price difference" : [
    NumberInt(100), 
    NumberInt(-100)
], 
"things" : [
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea4"), 
        "name" : "Laser Sable", 
        "datetime" : ISODate("2015-12-29T13:28:50.823+0000"), 
        "units" : NumberInt(-10), 
        "price" : NumberInt(-100), 
        "dayyear" : NumberInt(363), 
        "difference" : NumberInt(-10), 
        "price difference" : NumberInt(100), 
        "year" : NumberInt(2015)
    }, 
    {
        "_id" : ObjectId("56828a929da4bc16eb534ea6"), 
        "name" : "Laser Sable", 
        "datetime" : ISODate("2015-12-28T13:28:50.823+0000"), 
        "units" : NumberInt(7), 
        "price" : NumberInt(100), 
        "dayyear" : NumberInt(363), 
        "difference" : NumberInt(7), 
        "price difference" : NumberInt(-100), 
        "year" : NumberInt(2015)
    }
]
}

第 5 阶段：我将元素添加到“差异”数组中，以便得到 每个项目的单位日间差异。我也从其他中选择 创建的数组总是否定项（因为它们是 标记为“原件”），所以我可以得到原价和 每个项目每天的总单位

{ 
"_id" : ObjectId("56828a929da4bc16eb534ea7"), 
"difference" : NumberInt(0), 
"price difference" : NumberInt(0), 
"dayyear" : NumberInt(362), 
"year" : NumberInt(2015), 
"name" : "Flying Skateboard", 
"datetime" : [
    ISODate("2015-12-28T13:28:50.912+0000")
], 
"units" : NumberInt(1), 
"price" : NumberInt(50)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea6"), 
"difference" : NumberInt(0), 
"price difference" : NumberInt(0), 
"dayyear" : NumberInt(362), 
"year" : NumberInt(2015), 
"name" : "Laser Sable", 
"datetime" : [
    ISODate("2015-12-28T13:28:50.823+0000")
], 
"units" : NumberInt(7), 
"price" : NumberInt(100)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"difference" : NumberInt(-2), 
"price difference" : NumberInt(0), 
"dayyear" : NumberInt(363), 
"year" : NumberInt(2015), 
"name" : "Flying Skateboard", 
"datetime" : [
    ISODate("2015-12-29T13:28:50.912+0000"), 
    ISODate("2015-12-28T13:28:50.912+0000")
], 
"units" : NumberInt(3), 
"price" : NumberInt(50)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"difference" : NumberInt(-3), 
"price difference" : NumberInt(0), 
"dayyear" : NumberInt(363), 
"year" : NumberInt(2015), 
"name" : "Laser Sable", 
"datetime" : [
    ISODate("2015-12-29T13:28:50.823+0000"), 
    ISODate("2015-12-28T13:28:50.823+0000")
], 
"units" : NumberInt(10), 
"price" : NumberInt(100)
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea5"), 
"difference" : NumberInt(0), 
"price difference" : NumberInt(0), 
"dayyear" : NumberInt(364), 
"year" : NumberInt(2015), 
"name" : "Flying Skateboard", 
"datetime" : [
    ISODate("2015-12-29T13:28:50.912+0000")
], 
"units" : null, 
"price" : null
}
{ 
"_id" : ObjectId("56828a929da4bc16eb534ea4"), 
"difference" : NumberInt(0), 
"price difference" : NumberInt(0), 
"dayyear" : NumberInt(364), 
"year" : NumberInt(2015), 
"name" : "Laser Sable", 
"datetime" : [
    ISODate("2015-12-29T13:28:50.823+0000")
], 
"units" : null, 
"price" : null
}

最后，为了为每个元素保持正确的 ISODate，我 检查数组的哪个元素等效于“dayyear”字段。 如果数组中只有一个元素并且它不等于 “dayyear”，它将一天与 ISODate 元素相加（注意 “实际日期”将始终是一天或以下一天。

在这 6 个步骤之后，现在可以按月、年或名称进行分组了。 请注意，最后一个元素始终是剩余的“克隆”，日期为明天，但由于它们的所有字段都是 0 或 null，它们不会影响聚合度量（如总销售额等）但你必须采取制作平均值时要小心，因为它们会影响它们。希望对您有所帮助！

【讨论】：

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