CODEWITHSUNDEEP
javascript
Shivam_Yadav
Shivam_Yadav

Reputation: 204

How to use javascript (filter) to count the frequency of an object value?

This is the url from which i have to fetch data.I want the frequency of the postIds.How can i do this using the methods (map,filter or reduce).I've done it using a loop .Can it be done in a better way?.please help..

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
  fetch('http://jsonplaceholder.typicode.com/comments')
  .then(
    function(response) {
      if (response.status !== 200) {
        console.log('Looks like there was a problem. Status Code: ' +
          response.status);
        return;
      }
      response.json().then(function(data) 
      {
          var na=[];
          for(var i=1;i<=100;i++)
          {
            var a= data.filter(ab=> {
          return ab.postId==i;});
         // console.log(a); 
          na.push({PostId:i,frequency:a.length});
          }
          console.log(na);
      }
  )})
  .catch(function(err) {
    console.log('Fetch Error :-S', err);
  });
    </script>
</body>
</html>

Upvotes: -1

Views: 398

Answers (3)

sonEtLumiere
sonEtLumiere

Reputation: 4562

I hope this helps

let counterObj = {};

let cars = [
    { id: 1, name: 'Mercedes', year: '2015' },
    { id: 2, name: 'Mercedes', year: '2000' },
    { id: 3, name: 'BMW', year: '2010' },
    { id: 4, name: 'BMW', year: '2004' },
    { id: 5, name: 'Volvo', year: '2012' },
    { id: 6, name: 'Volvo', year: '2014' } 
];


for (let item of cars){
    counterObj[item.name] = 1 + (counterObj[item.name] || 0)
}

console.log(counterObj);

Upvotes: 2

slumbergeist
slumbergeist

Reputation: 1538

You can use reduce to generate a map of PostId with its frequency.

function mapFrequency(data) {
     return data.reduce((map, datum) => {
        if (map[datum.postId]) {
          map[datum.postId] += 1;
        } else {
          map[datum.postId] = 1 
        }
        return map;
        
     }, {})
}

This function will create an object with keys as postId and value as its frequency.

If you want to generate an array as in your sample, you can then do

 const frequencies = mapFrequency(data);
 const result = Object.keys(frequencies).map((id) => {
   return {
      PostId: id, 
      frequency: frequencies[id]
   }
  });

Upvotes: 1

Konstantin
Konstantin

Reputation: 55

With reduce you can do something like this:

const na = data.reduce((acc, el) => {
  acc[el.postId] = acc[el.postId] ? acc[el.postId] + 1 : 1;
  return acc;
}, {});

Pretty much the same as @sonEtLumiere suggested, but with reduce

Upvotes: 1

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