Group array by key and create an array of the related keys in each iteration

Question

Given an array of object

const data = [ 
  { id: 1,
    documentation_id: 4,
    document_id: 'nil',
    category_id: 1,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 11,
    documentation_id: 10,
    document_id: 'nil',
    category_id: 1,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 2,
    documentation_id: 5,
    document_id: '1',
    category_id: 2,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 100,
    documentation_id: 15,
    document_id: '10',
    category_id: 2,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 3,
    documentation_id: 5,
    document_id: '3',
    category_id: 3,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 4,
    documentation_id: 6,
    document_id: '1',
    category_id: 4,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 5,
    documentation_id: 6,
    document_id: '3',
    category_id: 5,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" },
  { id: 6,
    documentation_id: 6,
    document_id: '5',
    category_id: 1,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z" 
  },
  { id: 7,
    documentation_id: 7,
    document_id: '1',
    category_id: 6,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"}]

I want to be able to group by category_id such that result looks like this

const data = [{
    category_id: 1,
    documentation: [{
        document_id: "nil",
        documentation_id: 4
    }, {
        document_id: "nil",
        documentation_id: 10
    }, {
        document_id: "5",
        documentation_id: 6
    }]
}, {
    category_id: 2,
    documentation: [{
        document_id: "1",
        documentation_id: 5
    }, {
        document_id: "10",
        documentation_id: 15
    }]
}, {
    category_id: 3,
    documentation: [{
        document_id: "3",
        documentation_id: 5
    }]
}, {
    category_id: 4,
    documentation: [{
        document_id: "1",
        documentation_id: 6
    }]
}, {
    category_id: 5,
    documentation: [{
        document_id: "3",
        documentation_id: 6
    }]
}, {
    category_id: 6,
    documentation: [{
        document_id: "1",
        documentation_id: 7
    }]
}]

if the category exists more than once, create a documentation array and push the documentation in that category into the array. If the category exists once then push the only documentation for that category into the array.

This is the inefficient solution I came up with. I want to optimize the solution

function groupDocumentationByCategory(data) {
    const result = [];
    const formattedArray = data.slice(0);
    const seen = [];
    for (let k = 0; k < data.length; k++) {
        if (seen.indexOf(data[k].category_id) < 0) {
            seen.push(data[k].category_id);
            formattedArray[k].documentation = [];
            for (let j = 0; j < formattedArray.length; j++) {
                if (data[k].category_id === data[j].category_id) {
                    formattedArray[k].documentation.push({
                        document_id: formattedArray[j].document_id,
                        documentation_id: formattedArray[j].documentation_id,
                    });
                    delete data[k].documentation_id;
                    delete data[k].document_id;
                    delete data[k].created_at;
                    delete data[k].updated_at;
                }
            }
            result.push(data[k]);
        }
    }
    return result;
}

CertainPerformance · Accepted Answer · 2020-04-11 08:53:18Z

1

Iterate over the array and construct an object indexed by category_id. The first time an category_id is found, create the id and category_id properties, and initialize the documentation property to the empty array. Then push to that array. At the end, take the object's values:

const data=[{id:1,documentation_id:4,document_id:"nil",category_id:1,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:11,documentation_id:10,document_id:"nil",category_id:1,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:2,documentation_id:5,document_id:"1",category_id:2,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:100,documentation_id:15,document_id:"10",category_id:2,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:3,documentation_id:5,document_id:"3",category_id:3,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:4,documentation_id:6,document_id:"1",category_id:4,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:5,documentation_id:6,document_id:"3",category_id:5,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:6,documentation_id:6,document_id:"5",category_id:1,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"},{id:7,documentation_id:7,document_id:"1",category_id:6,created_at:"2020-03-29T11:06:44.000Z",updated_at:"2020-03-29T11:06:44.000Z"}];

const dataByCategory = {};
for (const { id, category_id, document_id, documentation_id } of data) {
  if (!dataByCategory[category_id]) {
    dataByCategory[category_id] = {
      id,
      category_id,
      documentation: []
    };
  }
  dataByCategory[category_id].documentation.push({ document_id, documentation_id });
}

console.log(Object.values(dataByCategory));

answered Apr 11, 2020 at 8:53

CertainPerformance

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2 Comments

sannimichaelse Over a year ago

What is the run time of this algorithm if I may ask. 0(n) ?

CertainPerformance Over a year ago

Yes, it's just a plain iteration through all elements of the original array, O(n)

Akshay Bande · Accepted Answer · 2020-04-11 09:13:09Z

You can use Array.prototype.reduce combined with some Array.prototype.map to achieve the result.

Maybe it can help.

var data = [{
    id: 1,
    documentation_id: 4,
    document_id: "nil",
    category_id: 1,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 11,
    documentation_id: 10,
    document_id: "nil",
    category_id: 1,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 2,
    documentation_id: 5,
    document_id: "1",
    category_id: 2,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 100,
    documentation_id: 15,
    document_id: "10",
    category_id: 2,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 3,
    documentation_id: 5,
    document_id: "3",
    category_id: 3,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 4,
    documentation_id: 6,
    document_id: "1",
    category_id: 4,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 5,
    documentation_id: 6,
    document_id: "3",
    category_id: 5,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 6,
    documentation_id: 6,
    document_id: "5",
    category_id: 1,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  },
  {
    id: 7,
    documentation_id: 7,
    document_id: "1",
    category_id: 6,
    created_at: "2020-03-29T11:06:44.000Z",
    updated_at: "2020-03-29T11:06:44.000Z"
  }
];

data = data.reduce((acc, val) => {
  if (acc[val.category_id]) {
    acc[val.category_id].push(val);
  } else {
    acc[val.category_id] = [val];
  }

  return acc;
}, {});

data = Object.values(data)
  .map(val => {
    delete val.created_at;
    delete val.updated_at;
    return val;
  })
  .reduce((acc, val) => {
    let documentation = val.map(v => ({
      document_id: v.document_id,
      documentation_id: v.documentation_id
    }));
    acc.push({
      category_id: val[0].category_id,
      documentation
    });
    return acc;
  }, []);

console.log(data);

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