How to get properties of one array of objects into another array of objects

Question

Here's what I've got. One array of objects:

var teachers = [{
               Year: 2016,
               FullName: "Matt",
               Age: 39
             },
             {
               Year: 2016,
               FullName: "Sara",
               Age: 25
             },
             ...
            ];

And another array of objects. These would be nested like so:

var students = [[
                  {
                    Year: 2016,
                    FullName: "Zoe"
                    Age: 8
                  }
                ],
                [
                  {
                    Year: 2016,
                    FullName: "Lulu"
                    Age: 9
                  },
                  {
                    Year: 2016,
                    FullName: "Leo",
                    Age: 13
                  }
                ],
                [ // empty array here
                ],
                [
                  {
                    Year: 2016,
                    FullName: "Lotta",
                    Age: 11
                  }
                ]
                ...
               ];

How they are organized is that students[0] is a student of teachers[0]. students[4] are students of teachers[4], and so forth.

What I was attempting to do what to take the FullName property, 'Students' in each student and put those values into an array of a new property of teachers called 'SundayStudents'. So what I'd end up with would be:

teachers = [{
             Year: 2016,
             FullName: "Matt",
             Age: 39,
             SundayStudents: ["Zoe"]
            },
            {
              Year: 2016,
              FullName: "Sara",
              Age: 25,
              SundayStudents: ["Lulu", "Leo"]
            },
             ...
          ];

I tried a nested for-loop, but the students array has varying numbers of objects in each sub-array, and it doesn't create an array for the new property. I think I'm stuck.

  for (var j = 0, leng = teachers.length; j < leng; j++) {
    for (var k = 0, lent = students.length; k < lent; k++)
      Teachers[i].SundayStudents = Students[j][k].FullName;
  }

Any hints are welcome.

You can use .push() to append to an array.

Michael Zhang
– Michael Zhang

2016-06-20 13:55:33 +00:00
Commented Jun 20, 2016 at 13:55 — Michael Zhang
– Michael Zhang, Commented Jun 20, 2016 at 13:55

Nina Scholz · Accepted Answer · 2016-06-20 13:57:20Z

1

You could just iterate and check if the target element exist. Then you could make a new property with the mapped names.

var teachers = [{ Year: 2016, FullName: "Matt", Age: 39 }, { Year: 2016, FullName: "Sara", Age: 25 }],
    students = [[{ Year: 2016, FullName: "Zoe", Age: 8 }], [{ Year: 2016, FullName: "Lulu", Age: 9 }, { Year: 2016, FullName: "Leo", Age: 13 }], [{ Year: 2016, FullName: "Lotta", Age: 11 }]];

students.forEach(function (a, i) {
    if (Array.isArray(a) && teachers[i]) {
        teachers[i].SundayStudents = a.map(function (b) {
            return b.FullName;
        });
    }
});

console.log(teachers);

answered Jun 20, 2016 at 13:57

Nina Scholz

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1 Comment

flimflam57 Over a year ago

I appreciate the use of map. Thanks for your time.

Damon · Accepted Answer · 2016-06-20 13:57:31Z

1

Don't overdo the loops. You can use the outer loop's index for both teachers and student arrays.

for (var i = 0; i < teachers.length; i++) {
  teachers[i].SundayStudents = []
  for (var j = 0; j < students[i].length; j++) {
    teachers[i].SundayStudents.push(students[i][j].FullName);
  }
}

answered Jun 20, 2016 at 13:57

Damon

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Comments

kirinthos · Accepted Answer · 2016-06-20 13:58:15Z

1

well, if all students' elements are arrays (a 2-dimensional array) then you just need to add one more for loop to scrape the inner array

teachers[i].SundayStudents = [];
for (var j = 0; j < teachers.length; j++) {
    for (var k = 0; k < students.length; k++) {
        var studentSub = students[k];
        for (var l = 0; l < studentSub.length; l++) {
            teachers[j].SundayStudents.push(students[k][l].FullName);
        }
    }
}

answered Jun 20, 2016 at 13:58

kirinthos

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Comments

Mustehssun Iqbal · Accepted Answer · 2016-06-20 13:58:36Z

You are using students.length in the inner for loop which should have been students[j].length because it is an array of array.

var teachers = [{
               Year: 2016,
               FullName: "Matt",
               Age: 39
             },
             {
               Year: 2016,
               FullName: "Sara",
               Age: 25
             }
            ]

var students = [[
                  {
                    Year: 2016,
                    FullName: "Zoe",
                    Age: 8
                  }
                ],
                [
                  {
                    Year: 2016,
                    FullName: "Lulu",
                    Age: 9
                  },
                  {
                    Year: 2016,
                    FullName: "Leo",
                    Age: 13
                  }
                ],
                [ // empty array here
                ],
                [
                  {
                    Year: 2016,
                    FullName: "Lotta",
                    Age: 11
                  }
                ]
                ]

for(var i = 0; i < teachers.length; i++){
    teachers[i].SundayStudents = []

    for(var j = 0; j < students[i].length; j++){
        teachers[i].SundayStudents[j] = students[i][j].FullName
    }
}

console.log(teachers)

RomanPerekhrest · Accepted Answer · 2016-06-20 14:16:32Z

1

The solution using Array.forEach and Array.map functions:

teachers.forEach(function(v, i, arr) { // arr - the array that forEach() is being applied to
    if (Array.isArray(students[i]) && students[i].length) { // check for non-empty array
        arr[i].SundayStudents = students[i].map((st) => st.FullName);
    }        
});

console.log(JSON.stringify(teachers, 0, 4));

The output:

[
    {
        "Year": 2016,
        "FullName": "Matt",
        "Age": 39,
        "SundayStudents": [
            "Zoe"
        ]
    },
    {
        "Year": 2016,
        "FullName": "Sara",
        "Age": 25,
        "SundayStudents": [
            "Lulu",
            "Leo"
        ]
    }
    ...
]

edited Jun 20, 2016 at 14:16

answered Jun 20, 2016 at 14:11

RomanPerekhrest

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Comments

score 1 · Accepted Answer · 2016-06-20 14:17:41Z

1

Loop through teachers. Copy the object. Add SundayStudents as array. Loop through students of the corresponding index and push the FullName to SundayStudents :

var teachers = [{
  Year: 2016,
  FullName: "Matt",
  Age: 39
}, {
  Year: 2016,
  FullName: "Sara",
  Age: 25
}];

var students = [
  [{
    Year: 2016,
    FullName: "Zoe",
    Age: 8
  }],
  [{
    Year: 2016,
    FullName: "Lulu",
    Age: 9
  }, {
    Year: 2016,
    FullName: "Leo",
    Age: 13
  }]
];

var r = [];

teachers.forEach(function(obj, i) {
  var o = {};
  o = obj;
  o.SundayStudents = [];
  students[i].forEach(function(d) {
    o.SundayStudents.push(d.FullName);
  });
  r.push(o);
});

console.log(r);

edited Jun 20, 2016 at 14:17

answered Jun 20, 2016 at 14:08

user3589620

1 Comment

flimflam57 Over a year ago

Huge thanks. Your answer helped understand what's going on.

Redu · Accepted Answer · 2016-06-20 14:43:35Z

This appears to be a simple job of maps.

var students = [[
                  {
                    Year: 2016,
                    FullName: "Zoe",
                    Age: 8
                  }
                ],
                [
                  {
                    Year: 2016,
                    FullName: "Lulu",
                    Age: 9
                  },
                  {
                    Year: 2016,
                    FullName: "Leo",
                    Age: 13
                  }
                ],
                [ // empty array here
                ],
                [
                  {
                    Year: 2016,
                    FullName: "Lotta",
                    Age: 11
                  }
                ]],
teachers = [{
             Year: 2016,
             FullName: "Matt",
             Age: 39
            },
            {
              Year: 2016,
              FullName: "Sara",
              Age: 25
            },
            {
             Year: 2016,
             FullName: "Yellow Beard",
             Age: 39
            },
            {
              Year: 2016,
              FullName: "Professor Oclitus",
              Age: 25
            },
          ];
          
teachers = teachers.map((t,i) => (t.SundayStudents = students[i].map(s => s.FullName),t));
console.log(teachers);

Wow.. i just noticed there was an answer exactly the same. So let me give an ES5 compatible version.

teachers = teachers.map(function(t,i) {
                                        t.SundayStudents = students[i].map(function(s) {
                                                                                         return s.FullName;
                                                                                       });
                                        return t;
                                      });

Kruga · Accepted Answer · 2016-06-20 14:10:26Z

0

Just because it's possible, here's a one line answer

teachers.map((t, i) => (t.sundayStudents = students[i].map(s => s.FullName), t));

answered Jun 20, 2016 at 14:10

Kruga

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