Filter nested array based on its nested values

Question

If I had the following data, how would I go about filtering the students array in each node using ES6 syntax, so it only returns students that have a particular value in subjects (eg. subject = 'English')?

Data:

[
  {
    "node": {
      "name": "Miss Jones",
      "students": [
        {
          "name": "John",
          "subjects": ["English", "Maths"]
        },
        {
          "name": "Sarah",
          "subjects": ["Geography"]
        }
      ]
    }
  },
  {
    "node": {
      "name": "Mr Hudson",
      "students": [
        {
          "name": "Joe",
          "subjects": ["Maths", "French"]
        },
        {
          "name": "Samantha",
          "subjects": ["English"]
        }
      ]
    }
  }
]

Expected output:

[
  {
    "node": {
      "name": "Miss Jones",
      "students": [
        {
          "name": "John",
          "subjects": ["English", "Maths"]
        }
      ]
    }
  },
  {
    "node": {
      "name": "Mr Hudson",
      "students": [
        {
          "name": "Samantha",
          "subjects": ["English"]
        }
      ]
    }
  }
]

Thanks!

Ele · Accepted Answer · 2018-10-09 00:19:43Z

You don't need the function map like other answers are suggesting, even when the handler is mutating the original array.

Just use the function forEach for looping and the function filter along with the function includes for checking the array subjects.

const arr = [  {    "node": {      "name": "Miss Jones",      "students": [        {          "name": "John",          "subjects": ["English", "Maths"]        },        {          "name": "Sarah",          "subjects": ["Geography"]        }      ]    }  },  {    "node": {      "name": "Mr Hudson",      "students": [        {          "name": "Joe",          "subjects": ["Maths", "French"]        },        {          "name": "Samantha",          "subjects": ["English"]        }      ]    }  }],
      subject = 'English';
  
arr.forEach(o => o.node.students = o.node.students.filter(s => s.subjects.includes(subject)));

console.log(arr);

.as-console-wrapper { max-height: 100% !important; top: 0; }

slider · Accepted Answer · 2018-10-08 23:40:01Z

1

Yes, you can do it with map and filter.

let nodes = [
  {
    "node": {
      "name": "Miss Jones",
      "students": [
        {
          "name": "John",
          "subjects": ["English", "Maths"]
        },
        {
          "name": "Sarah",
          "subjects": ["Geography"]
        }
      ]
    }
  },
  {
    "node": {
      "name": "Mr Hudson",
      "students": [
        {
          "name": "Joe",
          "subjects": ["Maths", "French"]
        },
        {
          "name": "Samantha",
          "subjects": ["English"]
        }
      ]
    }
  }
];

const englishNodes = nodes.map(n => {
  n.node.students = n.node.students.filter(s => s.subjects.includes('English'));
  return n;
});

console.log(englishNodes);

answered Oct 8, 2018 at 23:40

slider

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6 Comments

dduyduong Over a year ago

This would not correct for case students don't have English subject. It will return a node with empty students. Please see my answer

slider Over a year ago

Yes, I'm assuming every node has at least one student with English as a subject. If not you can always run filter on the top level array again to select only those nodes with a non empty students array.

Ele Over a year ago

Function map is definitely useless!

slider Over a year ago

@Ele not if you want to filter nodes further to include only those that have non empty students :D

Ele Over a year ago

@slider function map is for conversion rather than filtering objects.

|

Tarek Essam · Accepted Answer · 2018-10-09 00:35:47Z

1

I would filter the data using .map and .filter.

const data = [{ "node": { "name": "Miss Jones", "students": [{ "name": "John", "subjects": ["English", "Maths"] }, { "name": "Sarah", "subjects": ["Geography"] }] } }, { "node": { "name": "Mr Hudson", "students": [{ "name": "Joe", "subjects": ["Maths", "French"] }, { "name": "Samantha", "subjects": ["English"] }] } }];

const results = data.map(({ node }) => {
    const students = node.students.filter(student =>
        student.subjects.includes('English'));
    return {
        node: {
            ...node,
            students
        }
    };
});

console.log(results);

edited Oct 9, 2018 at 0:35

answered Oct 8, 2018 at 23:41

Tarek Essam

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4 Comments

dduyduong Over a year ago

This would not correct for case students don't have English. It will return a node with empty students. Please see my answer

Tarek Essam Over a year ago

Yes it will return an empty student array and that is the required, he only want the students with English subject.

Ele Over a year ago

Function map is definitely useless!

Tarek Essam Over a year ago

Now i am not mutating the original array. Is this better

dduyduong · Accepted Answer · 2018-10-08 23:52:03Z

0

What are you trying to do is transforming data, not only filter. Please try the following:

data.map((o) => {
  o.students = o.node.students.filter((s) => s.subjects.indexOf("English") >= 0);
  if (o.students.length >= 0) return o;
  return null;
}).filter((o) => o);

You have to return null for students that does not have English subject, then filter null to ignore them

answered Oct 8, 2018 at 23:52

dduyduong

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2 Comments

Ele Over a year ago

Function map is definitely useless!

dduyduong Over a year ago

@Ele Why it is useless?

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