Filter and sort a JavaScript array

Question

I have an array like this:

[{
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 6.4
    }
}, {
    "number": "3",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}, {
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}]

I am trying to create a new array with the following criteria:

Get highest rating (array.rating.average) of each number (array.number)

Output should be:

[{
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 6.4
    }
}, {
    "number": "3",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}
}]

I have just managed to sort by highest rating:

array.sort(function(a , b) {
    return a.rating.average - b.rating.average;
});
array.reverse();

But, now, I just only want one object per duplicate array.number, keeping the one that has the highest array.rating.average.

Possible duplicate with stackoverflow.com/questions/2722159/… and stackoverflow.com/questions/1129216/… — west efan
– west efan, Commented Sep 3, 2016 at 3:12
Since 3 and 4 have the same average rating. Any reason why number 3 is chosen over 4? — Samuel Toh
– Samuel Toh, Commented Sep 3, 2016 at 3:17
@SamuelToh I would like to have an array with each of the highest rating "number". — James
– James, Commented Sep 3, 2016 at 3:20
@westefan I have already gone through those 2 urls already, and both of them have different outcomes to what I am trying to do. — James
– James, Commented Sep 3, 2016 at 3:24

Haibara Ai · Accepted Answer · 2016-09-03 04:58:17Z

array.sort((a, b) => {
  if(a.number === b.number) {
    // If two elements have same number, then the one who has larger rating.average wins
    return b.rating.average - a.rating.average;
  } else {
    // If two elements have different number, then the one who has larger number wins
    return b.number - a.number;
  }
});


array = array.filter((element, index) => {
  return index === 0 || element.number !== array[index-1].number;
});

For your test case,

[{
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 6.4
  }
}, {
  "number": "3",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}, {
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}]

After sorting, the output would be

[{
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 6.4
  }
}, {
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}, {
  "number": "3",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}]

And after filter, the final result:

[{
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 6.4
  }
}, {
  "number": "3",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}]

jenish · Accepted Answer · 2019-05-13 07:07:35Z

1

Simply you can use lodash method for sort by anything that you want to sort by fileName, number, etc.

const _ = require('lodash');

var data = [{
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 6.4
  }
}, {
  "number": "3",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}, {
  "number": "4",
  "fileName": "fileXX",
  "rating": {
    "average": 5.4
  }
}]

var result = _.sortBy(data, ['number']);

console.log(result)

Output:
[ { number: '3', fileName: 'fileXX', rating: { average: 5.4 } },
  { number: '4', fileName: 'fileXX', rating: { average: 6.4 } },
  { number: '4', fileName: 'fileXX', rating: { average: 5.4 } } ]

answered May 13, 2019 at 7:07

jenish

1812 silver badges8 bronze badges

1 Comment

nihiser Over a year ago

The OP's desired output includes filtering out duplicates, which is missing.

Khiem Tran · Accepted Answer · 2016-09-03 04:37:27Z

First you create a dictionary for keeping the highest rating for each number:

var data = [{
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 6.4
    }
}, {
    "number": "3",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}, {
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}];


var filterMap = {};
data.forEach(function (item) {
  if (!filterMap[item.number] || filterMap[item.number].rating.average < item.rating.average) {
    filterMap[item.number] = item;
  }
})

var result = [];

for (var number in filterMap) {
  result.push(filterMap[number]);
}


result.sort(function(a , b) {
   return b.rating.average - a.rating.average;
});

console.log(result);

StardustGogeta · Accepted Answer · 2016-09-03 16:36:30Z

0

arr = [{
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 6.4
    }
}, {
    "number": "3",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}, {
    "number": "4",
    "fileName": "fileXX",
    "rating": {
        "average": 5.4
    }
}]

arr = arr.sort(function(a,b){return b.number-a.number || b.rating.average-a.rating.average}).filter(function(a,b,c){return !b || c[b-1].number != a.number});
console.log(arr);

I believe that this will solve your problem by sorting and filtering.

EDIT: Should now support older browsers.

edited Sep 3, 2016 at 16:36

answered Sep 3, 2016 at 3:23

StardustGogeta

3,3932 gold badges21 silver badges34 bronze badges

7 Comments

user663031 Over a year ago

Sort functions need to return -1, 0, or 1, not a boolean.

StardustGogeta Over a year ago

@tor A boolean evaluates to true or false, 1 and 0, therefore I do not see a problem. Additionally, it works, and is essentially the same as the answers after it.

user663031 Over a year ago

Please read the documentation for sort and the function to be passed to it. Returning the equivalent of 0 and 1 does work in some cases, but it does not work reliably.

StardustGogeta Over a year ago

@tor on both the w3schools.com/jsref/jsref_sort.asp and developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… sources, it has absolutely no mention of undefined behavior with booleans. When evaluating, it will check if true > 0, which will always return true.

user663031 Over a year ago

Educate yourself. stackoverflow.com/questions/24080785/…

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