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
– ste2425, Commented Jun 1, 2016 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
– Nemanja Todorovic, Commented Jun 1, 2016 at 10:21
Possible duplicate of Find the number of occurrences a given value has in an array — 1983
– 1983, Commented Jun 1, 2016 at 10:54
please have a look to What should I do when someone answers my question? — Nina Scholz
– Nina Scholz, Commented Jun 1, 2016 at 12:04

Nina Scholz · Accepted Answer · 2016-06-01 10:21:13Z

8

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 1, 2016 at 10:21

Nina Scholz

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2 Comments

Sandeep Nayak Over a year ago

Could you tell us how (r[a.overallLevel] || 0) + 1; will evaluate

ste2425 Over a year ago

@SandeepNayak r[a.overallLevel] || 0 will assign zero should r[a.overallLevel] be a fasly value. It will then add one to it.

Ali Mamedov · Accepted Answer · 2016-06-01 10:22:47Z

3

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}

answered Jun 1, 2016 at 10:22

Ali Mamedov

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