JavaScript code to get count of occurrence of objects in array of objects using array.reduce()

Question

var developers = [
    { name: "Joe", age: 23 ,overallLevel: "high"},
    { name: "Sue", age: 28 ,overallLevel: "advanced" },
    { name: "Jon", age: 32 ,overallLevel: "high" },
    { name: "Bob", age: 24 ,overallLevel: "high" },
    { name: "Bob", age: 20 ,overallLevel: "advanced" }
]

Need count of overallLevel in the mentioned array using array.reduce() [high:3, advanced:2]

What have you tried already? What issues are you facing? Generally speaking `Fix this for me` questions don't go down too well. — ste2425, Jun 01 '16 at 10:18
You could use filter() and just pass value of overallLevel to filter by. Than you could just count items in filtered array. — Nemanja Todorovic, Jun 01 '16 at 10:21
Possible duplicate of [Find the number of occurrences a given value has in an array](http://stackoverflow.com/questions/17313268/find-the-number-of-occurrences-a-given-value-has-in-an-array) — 1983, Jun 01 '16 at 10:54
please have a look to [What should I do when someone answers my question?](http://stackoverflow.com/help/someone-answers) — Nina Scholz, Jun 01 '16 at 12:04

score 7 · Answer 1 · answered Jun 01 '16 at 10:21

7

You could just count them with an object.

var developers = [{ name: "Joe", age: 23, overallLevel: "high" }, { name: "Sue", age: 28, overallLevel: "advanced" }, { name: "Jon", age: 32, overallLevel: "high" }, { name: "Bob", age: 24, overallLevel: "high" }, { name: "Bob", age: 20, overallLevel: "advanced" }],
    overallLevel = developers.reduce(function (r, a) {
        r[a.overallLevel] = (r[a.overallLevel] || 0) + 1;
        return r;
    }, {});

console.log(overallLevel);

answered Jun 01 '16 at 10:21

Nina Scholz

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Could you tell us how `(r[a.overallLevel] || 0) + 1;` will evaluate – Sandeep Nayak Jun 01 '16 at 10:29
1

@SandeepNayak `r[a.overallLevel] || 0` will assign zero should `r[a.overallLevel]` be a fasly value. It will then add one to it. – ste2425 Jun 01 '16 at 10:41

score 2 · Answer 2 · answered Jun 01 '16 at 10:22

Try this (you need no array.reduce() to do that):

var
  i,
  count = {high: 0, advanced: 0},
  developers = [
    { name: "Joe", age: 23 ,overallLevel: "high"},
    { name: "Sue", age: 28 ,overallLevel: "advanced" },
    { name: "Jon", age: 32 ,overallLevel: "high" },
    { name: "Bob", age: 24 ,overallLevel: "high" },
    { name: "Bob", age: 20 ,overallLevel: "advanced" }
  ];

for (i in developers) {

  count[developers[i].overallLevel]++;
}

alert(JSON.stringify(count)); //  Object { high=3,  advanced=2}

JavaScript code to get count of occurrence of objects in array of objects using array.reduce()

2 Answers2

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