Add count value to object with same key values (array of objects)

Question

Hello I have kind of complicated iteration to be done over an array of objects. I have array like this:

[ 
  { name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Jacob', lastName: 'Smith', dob: '1991-08-21' },
  { name: 'Ann', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Ann', lastName: 'Nansen', dob: '1983-01-01' },
  { name: 'Jacob', lastName: 'Smith', dob: '1985-06-15' },
  { name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Ann', lastName: 'Smith', dob: '2010-11-29' },
]

I would like to add count property to each object that counts objects with same name and surname... So it should be now:

[ 
  { name: 'Jacob', lastName: 'Smith', count: 4 },
  { name: 'Ann', lastName: 'Smith', count: 2 },
  { name: 'Ann', lastName: 'Nansen', count: 1' },
]

Nikhil Aggarwal · Accepted Answer · 2019-04-24 11:16:07Z

5

You can use Array.reduce and Object.values

Convert array in an object with key as name and last name combination with value being the resulting object.
From the object, get all values as the final result

let arr = [{ name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },{ name: 'Jacob', lastName: 'Smith', dob: '1991-08-21' },{ name: 'Ann', lastName: 'Smith', dob: '1995-11-29' },{ name: 'Ann', lastName: 'Nansen', dob: '1983-01-01' },{ name: 'Jacob', lastName: 'Smith', dob: '1985-06-15' },{ name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },{ name: 'Ann', lastName: 'Smith', dob: '2010-11-29' }];

let result = Object.values(arr.reduce((a,{name, lastName}) => {
  let key = `${name}_${lastName}`;
  a[key] = a[key] || {name, lastName, count : 0};
  a[key].count++;
  return a;
}, {}));

console.log(result);

answered Apr 24, 2019 at 11:16

Nikhil Aggarwal

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Jonas Wilms · Accepted Answer · 2019-04-24 11:15:03Z

0

  const hash = [];

  for(const { name, lastName } of persons) {
    const key = name + "/" + lastName;
    if(!hash[key]) hash[key] = {
      name,
      lastName,
      count: 0,
    };

    hash[key].count++;
 }

  const result = Object.values(hash);

answered Apr 24, 2019 at 11:15

Jonas Wilms

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1 Comment

Volod Over a year ago

'Try' is never the answer

trincot · Accepted Answer · 2019-04-24 11:21:55Z

You could use JSON.stringify to combine name and last name in a safe way. I like using a Map to group the records with the same keys together:

const data = [{ name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },{ name: 'Jacob', lastName: 'Smith', dob: '1991-08-21' },{ name: 'Ann', lastName: 'Smith', dob: '1995-11-29' },{ name: 'Ann', lastName: 'Nansen', dob: '1983-01-01' },{ name: 'Jacob', lastName: 'Smith', dob: '1985-06-15' },{ name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },{ name: 'Ann', lastName: 'Smith', dob: '2010-11-29' }];
const keyed = data.map(o => [JSON.stringify([o.name, o.lastName]), o]);
const map = new Map(keyed.map(([key, {name, lastName}]) => 
                              [key, {name, lastName, count: 0}]));
keyed.forEach(([key, o]) => map.get(key).count++);
const result = Array.from(map.values());

console.log(result);

Garach Ankur · Accepted Answer · 2019-04-24 11:40:03Z

let arr=[ 
  { name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Jacob', lastName: 'Smith', dob: '1991-08-21' },
  { name: 'Ann', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Ann', lastName: 'Nansen', dob: '1983-01-01' },
  { name: 'Jacob', lastName: 'Smith', dob: '1985-06-15' },
  { name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Ann', lastName: 'Smith', dob: '2010-11-29' },
];



let outerArr=[];

for(arrValue of arr)
{
  delete arrValue.dob

  let index=outerArr.findIndex(item=> item.name==arrValue.name && 
  item.lastName==arrValue.lastName);

  if(index==-1)
  {
	let arrFind=arr.filter(item=> item.name==arrValue.name && 
    item.lastName==arrValue.lastName)
     arrValue.count=arrFind.length
     outerArr.push(arrValue)
  }

}
	console.log('result',outerArr)

Francis Leigh · Accepted Answer · 2019-04-24 13:00:09Z

You can achieve this by reducing the original Array. As you iterate through the people you can check if they have already been "grouped" using Array.some - if they haven't, push your built person Object to the previously returned Array.

const getInstances = ({ name, lastName }, data) => data.filter(d => d.name === name && d.lastName === lastName).length

const people = [ 
  { name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Jacob', lastName: 'Smith', dob: '1991-08-21' },
  { name: 'Ann', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Ann', lastName: 'Nansen', dob: '1983-01-01' },
  { name: 'Jacob', lastName: 'Smith', dob: '1985-06-15' },
  { name: 'Jacob', lastName: 'Smith', dob: '1995-11-29' },
  { name: 'Ann', lastName: 'Smith', dob: '2010-11-29' },
]
  
const groupedPeople = people.reduce((group, person, i, people) => {
  const alreadyBeenGrouped = group.some(({ name, lastName }) => name === person.name && lastName === person.lastName)

  if (!alreadyBeenGrouped) {
    group.push({
      name: person.name,
      lastName: person.lastName,
      count: getInstances(person, people)
    })
  }

  return group
}, [])

console.log(groupedPeople)

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