Counting occurrences of particular property value in array of objects [duplicate]

Question

I would like to know how i can count the number of occurences on an array of object like this one :

[ {id : 12,  name : toto, }, {id : 12,  name : toto, }, {id : 42,  name : tutu, }, {id : 12,  name : toto, }, ] 

in this case i would like to have a function who give me this :

getNbOccur(id){ //don't know...//  return occurs; } 

and if i give the id 12 i would like to have 3.

How can i do that?

Answer 1

A simple ES6 solution is using filter to get the elements with matching id and, then, get the length of the filtered array:

const array = [    {id: 12, name: 'toto'},    {id: 12, name: 'toto'},    {id: 42, name: 'tutu'},    {id: 12, name: 'toto'},  ];    const id = 12;  const count = array.filter((obj) => obj.id === id).length;    console.log(count);

Edit: Another solution, that is more efficient (since it does not generate a new array), is the usage of reduce as suggested by @YosvelQuintero:

const array = [    {id: 12, name: 'toto'},    {id: 12, name: 'toto'},    {id: 42, name: 'tutu'},    {id: 12, name: 'toto'},  ];    const id = 12;  const count = array.reduce((acc, cur) => cur.id === id ? ++acc : acc, 0);    console.log(count);

Answer 2

You count

var arr = [    {id: 12, name: 'toto'},    {id: 12, name: 'toto'},    {id: 42, name: 'tutu'},    {id: 12, name: 'toto'}  ]    function getNbOccur(id, arr) {    var occurs = 0;        for (var i=0; i<arr.length; i++) {      if ( 'id' in arr[i] && arr[i].id === id ) occurs++;    }      return occurs;  }    console.log( getNbOccur(12, arr) )