Count duplicate values in an array and return count with an additional value using Javascript

Question

I've got the following array and I'd like to return a new array containing the count of the duplicate ids along with the value of the id:

const things = [
  {
    id: 1,
    title: 'Something',
    categoryId: 1,
    categoryTitle: 'Category 1'
  },
  {
    id: 2,
    title: 'Another thing',
    categoryId: 1,
    categoryTitle: 'Category 1'
  },
  {
    id: 3,
    title: 'Yet another thing',
    categoryId: 2,
    categoryTitle: 'Category 2'
  },
  {
    id: 4,
    title: 'One more thing',
    categoryId: 4,
    categoryTitle: 'Category 3'
  },
  {
    id: 5,
    title: 'Last thing',
    categoryId: 4,
    categoryTitle: 'Category 3'
  }
]

I've managed to put together a simple function that returns the count of duplicate ids (see below), but it also return the id (i.e. 1, 2, 4):

function categoriesCount (things) {
  const thingsMapped = things.map(thing => thing.categoryId)
  return thingsMapped.reduce((map, val) => {
    map[val] = (map[val] || 0) + 1
    return map
  }, {})
}

console.log('categoriesCount', categoriesCount(things))

Returns:

"categoriesCount" Object {
  1: 2,
  2: 1,
  4: 2
}

Whereas I'd like it to return:

"categoriesCount" Object {
  'Category 1': 2,
  'Category 2': 1,
  'Category 3': 2
}

Note: the category title's numeric value (e.g. Category 3) may not match it's id value (e.g. 4 with regards to Category 3).

What am I missing?

Many thanks in advance.

Shouldn't the last 2 objects' title be "Category 4" to get that output? — Kobe
– Kobe, Commented Dec 5, 2019 at 11:03
Is the key the category label or a generic "Category " label followed by the categoryId? — briosheje
– briosheje, Commented Dec 5, 2019 at 11:04
Replace all instances of map[val] with map['Categories ' + val]??? — Salman Arshad
– Salman Arshad, Commented Dec 5, 2019 at 11:05

Nina Scholz · Accepted Answer · 2019-12-05 11:08:43Z

3

You could take categoryTitle directly without mapping the array before.

function categoriesCount (things) {
    return things.reduce((hash, { categoryTitle }) => {
        hash[categoryTitle] = (hash[categoryTitle] || 0) + 1;
        return hash;
   }, {});
}

const things = [{ id: 1, title: 'Something', categoryId: 1, categoryTitle: 'Category 1' }, { id: 2, title: 'Another thing', categoryId: 1, categoryTitle: 'Category 1' }, { id: 3, title: 'Yet another thing', categoryId: 2, categoryTitle: 'Category 2' }, { id: 4, title: 'One more thing', categoryId: 4, categoryTitle: 'Category 3' }, { id: 5, title: 'Last thing', categoryId: 4, categoryTitle: 'Category 3' }]

console.log(categoriesCount(things));

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Dec 5, 2019 at 11:08

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

briosheje Over a year ago

categoryTitle seems somewhat wrong considering the output. It looks like (though it doesn't make much sense) he needs to concatenate a generic label category with the categoryId.

briosheje · Accepted Answer · 2019-12-05 11:14:14Z

You could just do that in a single Array.reduce shot, using destructuring to acquire the desired categoryTitle and to build the key accordingly.

The following code assumes the categoryTitle is consistent along the records and that you want to group by categoryTitle. If you don't want do to such, please specify that.

const things = [
  {
    id: 1,
    title: 'Something',
    categoryId: 1,
    categoryTitle: 'Category 1'
  },
  {
    id: 2,
    title: 'Another thing',
    categoryId: 1,
    categoryTitle: 'Category 1'
  },
  {
    id: 3,
    title: 'Yet another thing',
    categoryId: 2,
    categoryTitle: 'Category 2'
  },
  {
    id: 4,
    title: 'One more thing',
    categoryId: 4,
    categoryTitle: 'Category 3'
  },
  {
    id: 5,
    title: 'Last thing',
    categoryId: 4,
    categoryTitle: 'Category 3'
  }
];

const res = things.reduce((acc, {categoryTitle}) => {
   return acc[categoryTitle] = (acc[categoryTitle] || 0) + 1, acc;
}, {});
console.log('categoriesCount', res);

Gogul · Accepted Answer · 2019-12-05 11:13:52Z

0

Assuming your Category Title will be consistent

function categoriesCount (things) {
const thingsMapped = things.map(thing => thing.categoryId)
  return thingsMapped.reduce((map, val) => {
    map[val] = (map[val] || 0) + 1
    return map
  }, {})
}

answered Dec 5, 2019 at 11:13

Gogul

2982 silver badges14 bronze badges

Comments

Ele · Accepted Answer · 2019-12-05 11:18:16Z

0

I think the map function is not needed, and what is missing is to use the attr categoryTitle as key:

const things = [  {    id: 1,    title: 'Something',    categoryId: 1,    categoryTitle: 'Category 1'  },  {    id: 2,    title: 'Another thing',    categoryId: 1,    categoryTitle: 'Category 1'  },  {    id: 3,    title: 'Yet another thing',    categoryId: 2,    categoryTitle: 'Category 2'  },  {    id: 4,    title: 'One more thing',    categoryId: 4,    categoryTitle: 'Category 3'  },  {    id: 5,    title: 'Last thing',    categoryId: 4,    categoryTitle: 'Category 3'  }];
function categoriesCount (things) {
  return things.reduce((map, {categoryTitle}) => {
    map[categoryTitle] = (map[categoryTitle] || 0) + 1;
    return map
  }, {})
}

console.log('categoriesCount', categoriesCount(things))

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Dec 5, 2019 at 11:18

answered Dec 5, 2019 at 11:07

Ele

33.8k7 gold badges43 silver badges80 bronze badges

2 Comments

Neil Merton Over a year ago

The category title doesn't always match the categoryId, e.g. Category 3 has an id of 4, so what you've suggested would result in 'Category 4': 2, whereas I'm after 'Category 3': 2, so the full category title, not one derived from the id.

briosheje Over a year ago

@NeilMerton your original example suggested the opposite though.

Collectives™ on Stack Overflow

Count duplicate values in an array and return count with an additional value using Javascript

4 Answers 4

1 Comment

Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related