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        MongoDB计算不同的价值?

        时间:2023-10-02

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                • 本文介绍了MongoDB计算不同的价值?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                  问题描述

                  下面显示我的代码.我必须计算重复的不同值的次数.在这里,我在结果"中存储了不同的值.我使用 collection.count() 来计算,但它不起作用.请任何人告诉我我必须在哪里出错.非常感谢.

                  Here below show my code. I have to calculate the how many times distinct value repeated. Here i have store distinct value in "results".I used collection.count() to calculate but it's not work. please any one tell me where i have to mistake. Thank you very much .

                  var DistinctIntoSingleDB = function(Collection,arr,opt,distVal,callback){
                   Collection.find({}).distinct(distVal, function(err, results) {
                        if(!err && results){
                              console.log("Distinct Row Length :", results.length);
                              var a,arr1 = [];
                              for(var j=0; j<results.length; j++){
                                  collection.count({'V6': results[j]}, function(err, count) {
                                        console.log(count)
                                  });
                  
                                  arr1.push(results[j]+ " : " +a);
                              }
                              callback(results,arr1);
                        }else{
                             console.log(err, results);
                             callback(results);
                        }
                   });
                  

                  推荐答案

                  在集合 'col1' 上获取字段 'field1' 的不同值并写入单独的集合 'distinctCount'.如果集合很大,也允许使用磁盘空间.

                  To get occurrences of distinct values of a field 'field1' on a collection 'col1' and write to a separate collection 'distinctCount'. Also allow to use disk space in case the collection is huge.

                  db.col1.aggregate(
                            [{$group: {
                                _id: "$field1",
                                count: { $sum : 1 }
                              }}, {
                              $group: {
                                _id: "$_id",
                                count: { $sum : "$count" }
                              }},{
                                $out: "distinctCount"
                              }],
                           {allowDiskUse:true}
                  )
                  

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                  上一篇:给定一个 id 列表,查询集合中不存在哪些 id 的最佳方法是什么? 下一篇:在 NodeJS 中,如何从 mongodb 输出具有不同字段名称的结果?

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