CODEWITHSUNDEEP
javascriptarraysreactjsecmascript-6
Triyugi Narayan Mani
Triyugi Narayan Mani

Reputation: 3109

How to count number of occurrences of distinct values from an array of objects in Javascript?

I have an array of objects like below:

var array =
    [
        {"name":"abc","age":20}
        {"name":"abc","age":20}
        {"name":"abc","age":20}
        {"name":"xyz","age":21}
        {"name":"xyz","age":21}
    ]

I want to count the number of occurrences of distinct values like:

[3,2]

Assuming abc has 3 occurrences and xyz has 2 occurrences.

I am doing it in reactjs. I am able to get distinct values like [abc,xyz] using this answer.

ES6 syntax is preferred.

Upvotes: 8

Views: 17799

Answers (6)

isethi
isethi

Reputation: 755

This is one way to do it:

var array =
	[
		{"name":"abc","age":20},
		{"name":"abc","age":20},
		{"name":"abc","age":20},
		{"name":"xyz","age":21},
		{"name":"xyz","age":21}
	]


let yy = {}
array.map( el => {
	yy[el.name] = (yy[el.name] || 0) + 1
})

console.log(yy)

And this is another way:

var array =
	[
		{"name":"abc","age":20},
		{"name":"abc","age":20},
		{"name":"abc","age":20},
		{"name":"xyz","age":21},
		{"name":"xyz","age":21}
	]


let yy = {}
array.map( el => {
	if (yy[el.name] === undefined || yy[el.name] === 0) {
		yy[el.name] = 1
	} else {
		yy[el.name] = yy[el.name] + 1
	}
})

console.log(yy)

Upvotes: 0

mav-raj
mav-raj

Reputation: 771

Still if anyone looking for distinct counts stored in an array

var result = array.reduce( (acc, o) => (acc[o.name] = (acc[o.name] || 0)+1, acc), {} );
result = Object.values(result); // returns an array of values from the object
// result will be [3,2]

Upvotes: 0

ghilesZ
ghilesZ

Reputation: 1586

Quick answer : new Set(array).size.

Explanation (From MDN Web Docs):

The Set object lets you store unique values of any type, whether primitive values or object references

Upvotes: -1

Mayank Shukla
Mayank Shukla

Reputation: 104369

You can use forEach/map to iterate the array and store the count in another variable, Check this:

var array = [
     {"name" : "abc", "age" : 20},
     {"name" : "abc", "age" : 20},
     {"name" : "abc", "age" : 20},
     {"name" : "xyz", "age" : 21},
     {"name" : "xyz", "age" : 21},
];
    
let b = {};

array.forEach(el => {
    b[el.name] = (b[el.name] || 0) + 1;
})

console.log(b);

Upvotes: 4

LetterEh
LetterEh

Reputation: 26696

Map/Reduce to the rescue:

const frequency = array
  .map(({ name }) => name)
  .reduce((names, name) => {
    const count = names[name] || 0;
    names[name] = count + 1;
    return names;
  }, {});

// frequency: { abc: 3, xyz: 2 }

Upvotes: 6

trincot
trincot

Reputation: 350147

You'll need to know to which name a count belongs, so I propose not to output an array that gives you no clue about that, but an object keyed by names and with as value the corresponding count:

var result = array.reduce( (acc, o) => (acc[o.name] = (acc[o.name] || 0)+1, acc), {} );


var array =
    [
        {"name":"abc","age":20},
        {"name":"abc","age":20},
        {"name":"abc","age":20},
        {"name":"xyz","age":21},
        {"name":"xyz","age":21}
    ];
    
var result = array.reduce( (acc, o) => (acc[o.name] = (acc[o.name] || 0)+1, acc), {} );

console.log(result);

Upvotes: 25

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