比较数组元素，删除具有最低分数的元素 [英] Compare array elements,remove the one with the lowest score

问题描述

学校db有200份文件。我必须删除每个文档有类型：家庭作业和最低的分数。

  {
_id：0，
name：aimee Zank，
scores：
 [
 {
type：exam，
score：1.463179736705023 
}，
 {
type：quiz，
score：11.78273309957772 
}，
 {
type：homework，
score 6.676176060654615 
}，
 {
type：homework，
score：35.8740349954354 
} 
] 
} 
  

例如，

  {
type：homework，
score：6.676176060654615 
} 
   
 
必须删除，因为score = 6.6< 35.8 
 
 
 
我对所有文档进行了排序：
  db。 students.find（{scores.type：homework}）。sort（{scores.score：1}）
  
但我不知道如何删除具有最低分数和类型的文档：homework？ 
注意：如何通过不使用聚合方法来解决它？例如，通过排序然后更新。
解决方案
这可以通过几个步骤完成。第一步是使用具有最小分数的文档列表，使用   $ match   ，   $ unwind   和   $ group   运算符简化您的文档，以找到每个文档的最低分数：
  lowest_scores_docs = db .school.aggregate（[
 {$ match：{scores.type：homework}}，
 {$ unwind：$ scores}，{$ match ：{scores.type：homework}}，
 {$ group：{_id：$ _ id，lowest_score：{$ min：$ scores.score }第二步是循环遍历上面的字典，并使用  
 
 $ b < =http://docs.mongodb.org/manual/reference/operator/update/pull/ =nofollow>   $ pull   运算符在更新查询中从数组中删除元素，如下所示：
 结果为lowest_scores_docs [ $$$：{scores：{score：result [result]：
： lowest_score]}}}）
  
 
There are 200 documents in school db. I must remove each document which has "type":"homework" and the lowest score. 
    {
        "_id" : 0,
        "name" : "aimee Zank",
        "scores" :
        [
            {
                "type" : "exam",
                "score" : 1.463179736705023
            },
            {
                "type" : "quiz",
                "score" : 11.78273309957772
            },
            {
                "type" : "homework",
                "score" : 6.676176060654615
            },
            {
                "type" : "homework",
                "score" : 35.8740349954354
            }
        ]
    }
For example,here 
    {
        "type" : "homework",
        "score" : 6.676176060654615
    }
must be removed  as score = 6.6 < 35.8

I sorted all the documents like this:
db.students.find({"scores.type":"homework"}).sort({"scores.score":1})
But I do not know how then to remove the doc having the lowest score and type:homework??? 
 NOTE: how to solve it by not using aggregation method? E.g., by sorting and then updating.
解决方案
This can be done in a couple of steps. The first step is to grab a list of the documents with the minimum score by using the aggregation framework with $match, $unwind and $group operators that streamlines your documents to find the minimum score for each document:
lowest_scores_docs = db.school.aggregate([ 
    { "$match": {"scores.type": "homework"} },
    { "$unwind": "$scores" },  { "$match": {"scores.type": "homework"} },
    { "$group": { "_id":"$_id", "lowest_score": {"$min": "$scores.score" } } } ] )
The second step is to loop through the dictionary above and use the $pull operator in the update query to remove the element from the array as follows:
for result in lowest_scores_docs["result"]:
    db.school.update({ "_id": result["_id"] }, 
        { "$pull": { "scores": { "score": result["lowest_score"] } } } )


                        
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