Count the Distinct Properties in an Array of Objects

Question

I have the following array of objects

const users = [
 { name: 'Bob Johnson', occupation: 'Developer' },
 { name: 'Joe Davidson', occupation: 'QA Tester' },
 { name: 'Kat Matthews', occupation: 'Developer' },
 { name: 'Ash Lawrence', occupation: 'Developer' },
 { name: 'Jim Powers', occupation: 'Project Manager}]

I want to create an object that stores the unique counts of the different types of occupations, like so

{ developerCount: 3, qaTesterCount: 1, projectManagerCount: 1 }

My current solution is this long and drawn out method

let occupationCounts = {
  developerCount: 0,
  qaTesterCount: 0,
  projectManagerCount: 0
}

// Loop through the array and count the properties
users.forEach((user) => {
  switch(user.occupation){
    case 'Developer':
      occupationCounts.developerCount++;
      break;
      // and so on for each occupation
  }
});

This method will only grow for every new type of occupation I have to add.

Is there a simpler solution to this? (Pure javascript or Lodash Wizardry)

Any input is appreciated!

Scott Sauyet · Accepted Answer · 2018-09-26 14:06:46Z

Array.prototype.reduce should help here, so long as you're not wedded to the specific count names:

const users = [
 { name: 'Bob Johnson', occupation: 'Developer' },
 { name: 'Joe Davidson', occupation: 'QA Tester' },
 { name: 'Kat Matthews', occupation: 'Developer' },
 { name: 'Ash Lawrence', occupation: 'Developer' },
 { name: 'Jim Powers', occupation: 'Project Manager'}
]

const counts = users.reduce((counts, {occupation}) => {
  counts[occupation] = (counts[occupation] || 0) + 1;
  return counts
}, {})

console.log(counts)

While you could do something to alter those names, I wouldn't bother unless it really matters.

Edit

If you do really want those, you can get close with something like this:

const key = occupation[0].toLowerCase() +
            occupation.slice(1).replace(/\s/g, '') + 'Count'
counts[key] = (counts[key] || 0) + 1;

But even that generates "qATesterCount" instead of "qaTesterCount". Going further would be a real challenge to do generically.

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