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Possible Duplicate:
Sorting JavaScript Object by property value

I want to get the top results for some value within my JSON. Easier explained with the example:

var jsonData = {
  bom: [
        {
            "Component":"Some Thing",
            "Version":"Version ABC",
            "License":"License ABC",
        },
        {
            "Component":"Another Thing",
            "Version":"Version XYZ",
            "License":"License ABC",
        }, 
        etc ....
       ]
}

So my goal is to determine that "License ABC" or another has X number of occurrences and then I want to be able sort those key:val pairs to insert into into the DOM as "The top X most popular licenses are:

  • License ABC - 100
  • License XYZ - 70
  • License 123 - 25

Right now I have this:

var countResults = function() {
    var fileLicenses = [];

    for ( var i = 0, arrLen = jsonData.files.length; i < arrLen; ++i ) {
        fileLicenses.push(jsonData.files[i]["License"]);
    }

    keyCount = {};
    for(i = 0; i < fileLicenses.length; ++i) {
        if(!keyCount[fileLicenses[i]]) {
            keyCount[fileLicenses[i]] = 0;
        }

        ++keyCount[fileLicenses[i]];
    }

    console.log( keyCount );
}();

Which get's me most of what I want, an object with key : values 

{
    thisKey : 78,
    thatKey :125,
    another key : 200,
    another key : 272,
    another key : 45,
    etc ...
}

But I don't know how to do anything with that. I just need to sort the numeric right column and have the associated keys stay along for the ride. Thoughts? Thank you!

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1 Answer 1

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6

You can't sort an object by it's values. What you can do is to transform it to an array of objects and sort that instead. Something like:

var rank = function(items, prop) {

  //declare a key->count table
  var results = {}

  //loop through all the items we were given to rank
  for(var i=0;len=items.length;i<len;i++) {

    //get the requested property value (example: License)
    var value = items[i][prop];

    //increment counter for this value (starting at 1)
    var count = (results[value] || 0) + 1;
    results[value] = count;
  }

  var ranked = []

  //loop through all the keys in the results object
  for(var key in results) {

    //here we check that the results object *actually* has
    //the key. because of prototypal inheritance in javascript there's
    //a chance that someone has modified the Object class prototype
    //with some extra properties. We don't want to include them in the
    //ranking, so we check the object has it's *own* property.
    if(results.hasOwnProperty(key)) {

      //add an object that looks like {value:"License ABC", count: 2} 
      //to the output array
      ranked.push({value:key, count:results[key]}); 
    }
  }

  //sort by count descending
  return ranked.sort(function(a, b) { return b.count - a.count; });
}

Usage: 

var sorted = rank(jsonData.bom, "License");
var first = sorted[0].value;

/code not tested

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4 Comments

Thanks fencliff! Plugged it in and it works great. Still need some time to understand the logic but just what I needed. Thanks!
@Matt I added some comments to the code to explain the logic. If the solution works, don't forget to mark the answer as accepted!
Wow. Really appreciate the comments Fencliff. The solution worked great from the get go but, it's always better to understand what you're plugging in! This helps. Thanks again!
@Matt, you're welcome. I wouldn't use any code I found on the internet unless I understood it, either :)

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