下划线组通过嵌套对象元素

Question

我有一些带有嵌套对象的数据，需要使用underscoreJS对嵌套对象进行分组。

[
      {
        "_id": "58e28acba878a54951c84e36",
        "InId": "5809c226e41a193f4ffc1fa5",
        "StuID": "58185aacd7e86244252eb3f0",
        "ExamList": {
          "Type": "FinalMk",
          "SchdlId": "58e28acba878a54951c84dd0",
          "Exams": {
            "SubjId": "5825803ec4a0aff62070d9f5",
            "MaxMark": 100,
            "PassMark": 50,
            "ExDate": "2016-08-11T18:30:00.000Z",
            "Mark": 62
          }
        }
      },
      {
        "_id": "58e28acba878a54951c84e36",
        "InId": "5809c226e41a193f4ffc1fa5",
        "StuID": "58185aacd7e86244252eb3f0",
        "ExamList": {
          "Type": "FinalMk",
          "SchdlId": "58e28acba878a54951c84dd0",
          "Exams": {
            "SubjId": "5825803ec4a0aff62070d9f6",
            "MaxMark": 100,
            "PassMark": 50,
            "ExDate": "2016-08-09T18:30:00.000Z",
            "Mark": 76
          }
        }
      },
    ],
    [
      {
        "_id": "58e28acba878a54951c84e4d",
        "InId": "5809c226e41a193f4ffc1fa5",
        "StuID": "58185aacd7e86244252eb3ec",
        "ExamList": {
          "Type": "FinalMk",
          "SchdlId": "58e28acba878a54951c84dd0",
          "Exams": {
            "SubjId": "5825803ec4a0aff62070d9f5",
            "MaxMark": 100,
            "PassMark": 50,
            "ExDate": "2016-08-11T18:30:00.000Z",
            "Mark": 59
          }
        }
      },
      {
        "_id": "58e28acba878a54951c84e4d",
        "InId": "5809c226e41a193f4ffc1fa5",
        "StuID": "58185aacd7e86244252eb3ec",
        "ExamList": {
          "Type": "FinalMk",
          "SchdlId": "58e28acba878a54951c84dd0",
          "Exams": {
            "SubjId": "5825803ec4a0aff62070d9f6",
            "MaxMark": 100,
            "PassMark": 50,
            "ExDate": "2016-08-09T18:30:00.000Z",
            "Mark": 56
          }
        }
      },
    ],

在这里，我必须使用“ SubjId”对嵌套对象进行分组

我尝试使用这些代码bt ourput是未定义的“考试”。

var groupBySubj = _.groupBy(docs.ExamList.Exams, 'SubjId');

Answer 1

要按嵌套属性分组，可以使用一个函数：

_.groupBy(data, function(student) { return student.ExamList.Exams.SubjId; })