How to re arrange an array in TypeScript

Question

I have an array with objects like below,

var users = [{
    id: 1,
    name: 'Swamy',
    category_id: 1,
    category_name: "Male"
  },
  {
    id: 2,
    name: 'Mahesh',
    category_id: 1,
    category_name: "Male"
  },
  {
    id: 3,
    name: 'Kajal',
    category_id: 2,
    category_name: "Female"
  },
  {
    id: 4,
    name: 'Rasi',
    category_id: 2,
    category_name: "Female"
  }
]

I want to re arrange the above based on category

var cat_users = [{
    category_id: 1,
    category_name: "Male",
    users: [{
      id: 1,
      name: 'Swamy'
    }, {
      id: 2,
      name: 'Mahesh'
    }]
  },
  {
    category_id: 2,
    category_name: "Female",
    users: [{
      id: 3,
      name: 'Kajal'
    }, {
      id: 4,
      name: 'Rasi'
    }]
  },
]

I am looking for a solution and cannot seem to find anything related. Please help in rearranging the array.

Array comes with a sort function, to which you can provide a function for a custom compare. Example here. — loremdipso
– loremdipso, Commented Oct 14, 2020 at 1:46
Search for "group by" and you'll find lots of similar questions. — Bergi
– Bergi, Commented Oct 14, 2020 at 1:48

John Michael Manlupig · Accepted Answer · 2020-10-14 02:03:15Z

You have to find if the category_id exists in your sorted array. If not then push a new entry. If yes then add the user to the users of that entry.

interface User {
    id: number;
    name: string;
};

interface Category {
    category_id: number;
    category_name: string;
}

interface Entry extends User, Category { }

interface SortedEntry extends Category {
    users: Array<User>;
}

var users: Array<Entry> = [
    {
        id: 1,
        name: 'Swamy',
        category_id: 1,
        category_name: "Male"
    },
    {
        id: 2,
        name: 'Mahesh',
        category_id: 1,
        category_name: "Male"
    },
    {
        id: 3,
        name: 'Kajal',
        category_id: 2,
        category_name: "Female"
    },
    {
        id: 4,
        name: 'Rasi',
        category_id: 2,
        category_name: "Female"
    }
];

const sorted: Array<SortedEntry> = [];

for (const { id, name, category_name, category_id } of users) {
    const match = sorted.find((entry) => entry.category_id === category_id);
    if (!match) {
        sorted.push({
            category_id,
            category_name,
            users: [
                {
                    id,
                    name,
                }
            ]
        });
    }
    else {
        match.users.push({
            id,
            name,
        });
        const index = sorted.indexOf(match);
        sorted[index] = match;
    }
}

console.log(sorted);

Derek Wang · Accepted Answer · 2020-10-14 01:47:34Z

First, based on input, you can group that input by category_id using Array.reduce.

And from that groupedBy object, you can generate the result you want using Array.map.

var users = [{
    id: 1,
    name: 'Swamy',
    category_id: 1,
    category_name: "Male"
  },
  {
    id: 2,
    name: 'Mahesh',
    category_id: 1,
    category_name: "Male"
  },
  {
    id: 3,
    name: 'Kajal',
    category_id: 2,
    category_name: "Female"
  },
  {
    id: 4,
    name: 'Rasi',
    category_id: 2,
    category_name: "Female"
  }
];

const groupBy = users.reduce((acc, cur) => {
  acc[cur.category_id] ? acc[cur.category_id].users.push({
    id: cur.id,
    name: cur.name
  }) : acc[cur.category_id] = {
    category_id: cur.category_id,
    category_name: cur.category_name,
    users: [{
      id: cur.id,
      name: cur.name
    }]
  };
  return acc;
}, {});

const result = Object.entries(groupBy).map(([ category_id, rest ]) => ({
  category_id,
  ...rest
}));
console.log(result);

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