How to return key of object with higher value in Javascript?

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8

Let’s say I have the following object:

var obj = {"frutas": 50, "vegetais": 100, "carnes": 150 };

How could I return the key of the highest value item? Example:

obj.maxKey(); // "carnes"

I tested some functions that deal with arrays, but apparently they do not work with objects in the pattern key: value, example:

Math.max.apply(null, meuArrayAqui);

So, how I could return the key of the highest value item?

javascript jquery

  • Accepts the use of frameworks?

  • @Fernando jQuery yes, but not third-party plugins.

  • uhm! I was thinking in that, but now that I realize that in your case is not an array but an object, and this only works for array? Or it can be with array?

3 answers

6


There is no native function for this, so you will need to check all values to find the largest:

var obj = {"frutas": 50, "vegetais": 100, "carnes": 150 };
var maior = -Infinity;
var chave;
for(var prop in obj) {
    // ignorar propriedades herdadas
    if(obj.hasOwnProperty(prop)) { 
         if(obj[prop] > maior) {
             maior = obj[prop];
             chave = prop;
         }
    }
}
alert(chave);

That’s the principle. Of course, for real use, it’s better to wrap it in a function. Depending on the desired use, one can still do some optimizations.

  • Great answer, I chose it as correct because I do not need third party libraries and because I do not persist the values of the object in case of reuse of the function.

3

The simplest way seems to me to be with a loop even, but if you seek a more functional alternative, it can be done as follows:

  • Get all object keys by using Object.keys;
  • Sort them in descending order of value (you need to use a custom function for this);
  • Take the first element.

Example:

var obj = {"frutas": 50, "vegetais": 100, "carnes": 150 };

var maior = Object.keys(obj).sort(function(a,b) {
                return obj[a] > obj[b] ? -1 :
                       obj[b] > obj[a] ? 1 : 0;
            })[0];

document.querySelector("body").innerHTML += "<p>" + maior + "</p>";

  • 1

    I took a test and found that this is quite slow. Slower than using jQuery for the loop.

  • 1

    @bfavaretto It does not surprise me, given what ordination is n*log(n), while the rest are just n... If AP hadn’t explicitly said it didn’t want third-party frameworks, I would suggest _.max, which makes it possible to establish an arbitrary criterion for max without having to perform unnecessary operations. Anyway, a simple loop should be faster than any more sophisticated alternative.

  • 1

    Yeah, the underscore was the first thing I thought. Maybe in ES7 (!) there is one Object.values, then you could do something cleaner (which is a great quality of your solution).

2

Using the each of jQuery and traversing through all objects, can do as follows:

function getKeyOfMaxObjValue(obj){
  // Variável que armazenará a maior key.
  var key;
  // Variável auxiliar para checar os valores
  var value = 0;
  $.each(obj, function(idx, val){
    // Se o valor atual da iteração é maior que o auxiliar
    if(val > value){
      // Atualiza o valor da variável auxiliar
      value = val;
      // Atribue a nova key
      key = idx;
    }
  });
  return key;
}

  • Solution very clean, but when I use the function then with an object of different values, it keeps returning the result of the first object I used.

  • @mgibsonbr I tested it on that flash drive, but I ended up replacing it with the solution marked "correct" because of the problem mentioned above. You can change the function there for this to reproduce what I commented.

  • 1

    @mgibsonbr Actually, I re-tested here and the error did not reproduce again, funny that it was only change the function that it had disappeared the first time. Anyway, I’ll remove the comments.

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