combine objects with same id in array of objects in javascript

Question

I have the following array of objects

[{
    "school_id": "s1",
    "school_name": "school1",
    "district_id": "d1",
    "students": [{
        "student_id": "1",
        "student_name": "tony"
    }, {
        "student_id": "2",
        "student_name": "tom"
    }]
}, {
    "school_id": "s2",
    "school_name": "school2",
    "district_id": "d2",
    "students": [{
        "student_id": "1",
        "student_name": "march"
    }, {
        "student_id": "2",
        "student_name": "alex"
    }]
}, {
    "school_id": "s3",
    "school_name": "school3",
    "district_id": "d3",
    "students": [{
        "student_id": "1",
        "student_name": "bill"
    }, {
        "student_id": "2",
        "student_name": "bob"
    }]
}, {
    "school_id": "s4",
    "school_name": "school4",
    "district_id": "d3",
    "students": {
        "student_id": "1",
        "student_name": "tim"
    }
}]

I need to generate new repsonse by combining students belonging to the same school in the sae district as shown below

[{
    "district_id": "d1",
    "schoolList": [{
        "school_id": "s1",
        "school_name": "school1",
        "studentList": [{
            "student_id": "1",
            "student_name": "tony"
        }, {
            "student_id": "2",
            "student_name": "tom"
        }]
    }]
}, {
    "district_id": "d2",
    "schoolList": [{
        "school_id": "s2",
        "school_name": "school2",
        "studentList": [{
            "student_id": "1",
            "student_name": "march"
        }, {
            "student_id": "2",
            "student_name": "alex"
        }]
    }]
}, {
    "district_id": "d3",
    "schoolList": [{
        "school_id": "s3",
        "school_name": "school3",
        "studentList": [{
            "student_id": "1",
            "student_name": "bill"
        }, {
            "student_id": "1",
            "student_name": "bill"
        }]
    }, {
        "school_id": "s4",
        "school_name": "school4",
        "studentList": {
            "student_id": "1",
            "student_name": "tim"
        }
    }]
}]

How do I achieve it?

In the code you pasted for your object, for most items `students` is an array but for the last one it is an object; is that correct? It would be better if data are consistent therefore and `students` is always an array, even if there is just one student. — secan, Jul 21 '23 at 07:31

score 0 · Answer 1 · answered Jul 21 '23 at 07:43

It is my solution.

let data = [{
  "school_id": "s1",
  "school_name": "school1",
  "district_id": "d1",
  "students": [{
    "student_id": "1",
    "student_name": "tony"
  }, {
    "student_id": "2",
    "student_name": "tom"
  }]
}, {
  "school_id": "s2",
  "school_name": "school2",
  "district_id": "d2",
  "students": [{
    "student_id": "1",
    "student_name": "march"
  }, {
    "student_id": "2",
    "student_name": "alex"
  }]
}, {
  "school_id": "s3",
  "school_name": "school3",
  "district_id": "d3",
  "students": [{
    "student_id": "1",
    "student_name": "bill"
  }, {
    "student_id": "2",
    "student_name": "bob"
  }]
}, {
  "school_id": "s4",
  "school_name": "school4",
  "district_id": "d3",
  "students": {
    "student_id": "1",
    "student_name": "tim"
  }
}];
let temp = {};
let result = [];
data.forEach(d => {
  if (temp[d.district_id] === undefined) {
    temp[d.district_id] = [];
  }
  temp[d.district_id].push({
    "school_name": d.school_name,
    school_id: d.school_id,
    students: d.students
  });
});
for (const [key, value] of Object.entries(temp)) {
  result.push({
    "district_id": key,
    school_list: value
  });
}
console.log(result)

Hoang Long · Answer 2 · 2023-07-21T07:37:14.883

To achieve the desired result of combining students belonging to the same school in the same district, you can use JavaScript to iterate through the original array of objects and create a new response array based on the district and school information. Here's a step-by-step solution:

    // Original array of objects
    const data = [
      {"school_id":"s1","school_name":"school1","district_id":"d1","students":[{"student_id":"1","student_name":"tony"},{"student_id":"2","student_name":"tom"}]},
      {"school_id":"s2","school_name":"school2","district_id":"d2","students":[{"student_id":"1","student_name":"march"},{"student_id":"2","student_name":"alex"}]},
      {"school_id":"s3","school_name":"school3","district_id":"d3","students":[{"student_id":"1","student_name":"bill"},{"student_id":"2","student_name":"bob"}]},
      {"school_id":"s4","school_name":"school4","district_id":"d3","students":{"student_id":"1","student_name":"tim"}}
    ];
    
    // Create a new response array by combining students belonging to the same school in the same district
    const response = [];
    const districtMap = {};
    
    data.forEach((item) => {
      const { district_id, school_id, school_name, students } = item;
      
      // Check if the district already exists in the response array
      if (!districtMap[district_id]) {
        // If the district doesn't exist, add it to the response array
        districtMap[district_id] = {
          district_id,
          schoolList: []
        };
        response.push(districtMap[district_id]);
      }
      
      // Check if the school already exists in the district's schoolList
      const school = districtMap[district_id].schoolList.find((school) => school.school_id === school_id);
      if (!school) {
        // If the school doesn't exist, add it to the schoolList
        districtMap[district_id].schoolList.push({
          school_id,
          school_name,
          studentList: Array.isArray(students) ? students : [students]
        });
      } else {
        // If the school already exists, add students to its studentList
        school.studentList = school.studentList.concat(Array.isArray(students) ? students : [students]);
      }
    });
    
    console.log(JSON.stringify(response, null, 2));

score -2 · Answer 3 · answered Jul 21 '23 at 07:28

You can collect the unique districts ids as keys of a plain object, and associate the result object to each. Upon the first encounter of a district id, create the object for it (with empty schoolList array). Add each school to the schoolList array that corresponds to the district:

const data = [{"school_id":"s1","school_name":"school1","district_id":"d1","students":[{"student_id":"1","student_name":"tony"},{"student_id":"2","student_name":"tom"}]},{"school_id":"s2","school_name":"school2","district_id":"d2","students":[{"student_id":"1","student_name":"march"},{"student_id":"2","student_name":"alex"}]},{"school_id":"s3","school_name":"school3","district_id":"d3","students":[{"student_id":"1","student_name":"bill"},{"student_id":"2","student_name":"bob"}]},{"school_id":"s4","school_name":"school4","district_id":"d3","students":{"student_id":"1","student_name":"tim"}}]

const districts = {};
for (const {district_id, ...school} of data) {
    (districts[district_id] ??= { district_id, schoolList: [] })
        .schoolList.push(school);
}
const result = Object.values(districts);

console.log(result);

combine objects with same id in array of objects in javascript

3 Answers3