JavaScript using reduce to create object with counts, from array

Question

I'm trying to solve this little problem, where I need to use reduce to create an object with the counts of each item.

I thought I understood how reduce works, using a function to get multiple values down to one, yet I cannot figure out how this is to work.

Any ideas or advice? I really appreciate it.

// var people = ['josh', 'dan', 'sarah', 'joey', 'dan', 'josh', 'francis', 'dean'];

// can reduce be used to get: 

// { 
//   josh: 2,
//   dan: 2, 
//   sarah: 1,
//   joey: 1,
//   francis: 1,
//   dean: 1
// }

Nina Scholz · Accepted Answer · 2018-03-31 21:16:08Z

4

As you see, you need an object as result set for the count of the items of the array.

For getting the result, you could take a default value of zero for adding one to count the actual value, while you use the given name as property for counting.

var people = ['josh', 'dan', 'sarah', 'joey', 'dan', 'josh', 'francis', 'dean'],
    counts = people.reduce(function (c, p) {
        c[p] = (c[p] || 0) + 1;
        return c;
    }, Object.create(null));
    
console.log(counts);

answered Mar 31, 2018 at 21:16

Nina Scholz

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Dan Zuzevich · Accepted Answer · 2018-03-31 21:30:05Z

0

const groupedByName = people.reduce((obj, person) => {
  const count = obj[person] || 0
  return { ...obj, [person]: count + 1 }
}, {})

Working codepen

answered Mar 31, 2018 at 21:30

Dan Zuzevich

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1 Comment

Dan Zuzevich Over a year ago

This was from a functional programming course I am taking. I thought it was nice.

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