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JavaScript

Posted by shu Chan
shu Chan
2,951 Points

sorting an array of objects using callbacks

Hello! I'm having a hard time figuring out how to sort an array of objects based using callback functions

var list = [{id: "102", name: "Alice"},
            {id: "205", name: "Bob", title: "Dr."},
            {id: "592", name: "Clyde", age: 32}];

here is my code, my problem is I don't know how to check for values that are repeated in the key and group them together 

function groupBy(arr, cb) {

  let newObject = {}
  let array2 = []

  for(var i = 0; i < arr.length; i++){
      if(cb(arr[i]) === cb(arr[i])){
        array2.push(arr[i])
          newObject[cb(arr[i])] = array2
      } else {

        let array = [];
        array.push(arr[i])
        newObject[cb(arr[i])] = array
      }
  }
    console.log(newObject)
    return newObject
}

here are the functions calls and expected results:

groupBy(list, function(i) { return i.name.length; });

Returns:

  {
    "3": [{id: "205", name: "Bob", title: "Dr."}],
    "5": [{id: "102", name: "Alice"},
          {id: "592", name: "Clyde", age: 32}]
  }

groupBy(list, function(i) { return i.name.length; }

Returns:

  {
    "102": [{id: "102", name: "Alice"}],
    "205": [{id: "205", name: "Bob", title: "Dr."}],
    "592": [{id: "592", name: "Clyde", age: 32}]
  }

Please someone help!

2 Answers

Thomas Nilsen
Thomas Nilsen
14,957 Points

I answered a similar question a while back, so I'll just copy my answer in here:

var list = [{id: "102", name: "Alice"}, {id: "205", name: "Bob", title: "Dr."}, {id: "592", name: "Clyde", age: 32}];

function groupBy(arr, callback) {
    //Object that will contain the key/val pairs
    var result = {};
    //Loop through the arr we passed in
    arr.forEach(obj => {
        //When we execute our callback function
        //We get back the value we want to groupBy
        var key = callback(obj);
        //If the key does NOT exist in the object,
        //then create it and set it equal an empty array
        if(!result.hasOwnProperty(key)) {
            result[key] = [];
        }
        //Push the object that corresponds to our key
        result[key].push(obj);
    });

    //We have our answer. 
    return result;
}

console.log(groupBy(list, function(obj) {
    return obj.id;
}));


/*
This prints:

{ '102': [ { id: '102', name: 'Alice' } ],
  '205': [ { id: '205', name: 'Bob', title: 'Dr.' } ],
  '592': [ { id: '592', name: 'Clyde', age: 32 } ] }
*/
shu Chan
shu Chan
2,951 Points
shu Chan
shu Chan
2,951 Points

Thanks so much, I spent 7 hours doing work arounds....