使用Javascript在JSON文件中查找最常用的值

Question

I have a JSON file set up as follows

"mediaPosts": [
  {
      "index": 0,
      "source": "Twitter",
      "post": "commodo cillum in ut aliquip ad commodo esse duis sunt pariatur nostrud quis quis magna non ipsum Lorem cupidatat laboris",
      "sentiment": "Positive",
      "date": "24/05/2014",
      "gender": "Male",
      "age": 30,
      "country": "Gabon"
  },....]

The file contains 4000 records.

What I would like to know is what would be the best way to find 5 countries that appear the most in this JSON file

The only way I can think to do this is the following:

1.Create a variable for every country in the world (This would mean the creation of a wopping 196 variables)

2.Loop through my JSON list

for (i = 0; i < postObject.mediaPosts.length; i++)

3. Check the country string value for each record and increase the count of the corresponding country variable

   if (postObject.mediaPosts[i].country == "Afghanistan") {afghanistan++;} else if (postObject.mediaPosts[i].country == "Albania") {albania++;}

4. Then find the 5 largest values amogst my country variables

However this process feels very cumbersome so I was wondering if there is a better way to do this>

Answer 1

var countries = {};

for (i = 0; i < postObject.mediaPosts.length; i++) {
    var country = postObject.mediaPosts[i].country;
    countries[country] = countries[country] ? countries[country] + 1 : 1
}

then you will have an object (an associative array) of the countries as keys, and their count in the input object. Something like this:

countries = {
    "Afghanistan" : 5,
    "Albania" : 3,
    "Bulgaria" : 2,
    //... the other countries
}

From there you can loop over it and create pairs from it

var countryCountPairs = {};

for (country in countries) {
    countryCountPairs.push({country : country,  count : countries[country]});
}

Which will get you a data structure like this:

countryCountPairs = {
    { country : "Afghanistan",  count : 5 },
    { country : "Albania",  count : 3 },
    { country : "Bulgaria",  count : 2 },
    //... the other countries
}

And that is easily sortable:

countryCountPairs.sort(function(a, b) {
    // I think biggest value comes first with this, but you will have to test it. 
    return b.count - a.count;  
});

Which will give you a sorted version of the above.