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' },
]

Answer 1

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); 

Answer 2

  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);

Answer 3

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); 

Answer 4

 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) 

Answer 5

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)