Counting hash values in JavaScript/NodeJS/Underscore

Question

Counting hash values in JavaScript/NodeJS/Underscore

I have an array of hashed in Ruby that looks like this:

domains = [
 { "country" => "Germany"},
 {"country" => "United Kingdom"},
 {"country" => "Hungary"},
 {"country" => "United States"},
 {"country" => "France"},
 {"country" => "Germany"},
 {"country" => "Slovakia"},
 {"country" => "Hungary"},
 {"country" => "United States"},
 {"country" => "Norway"},
 {"country" => "Germany"},
 {"country" => "United Kingdom"},
 {"country" => "Hungary"},
 {"country" => "United States"},
 {"country" => "Norway"}
]

Edit::

So if it's returned in this format (from CouchDB):

domains= {"total_rows":55717,"offset":0,"rows": [
    {"country":"Germany"},  
    {"country":"United Kingdom"},
    {"country":"Hungary"},
    {"country":"United States"},\   \ 
    {"country":"France"},
    {"country":"Germany"},
    {"country":"Slovakia"},
    {"country":"Hungary"},
    {"country":"United States"},
    {"country":"Norway"},
    {"country":"Germany"}, 
    {"country":"United Kingdom"},
    {"country":"Hungary"}, 
    {"country":"United States"},
    {"country":"Norway"}]
}

How can I apply the same process. i.e. Get to the Item embedded within the array?

Using Ruby I can interate over the array and remove the duplicate values like this:

counted = Hash.new(0)
domains.each { |h| counted[h["country"]] += 1 }
counted = Hash[counted.map {|k,v| [k,v.to_s] }]

Which output something like this:

{"Germany"=>"3",
 "United Kingdom"=>"2",
 "Hungary"=>"3",
 "United States"=>"3",
 "France"=>"1",
 "Slovakia"=>"1",
 "Norway"=>"2"}

My question is what is the best way to achieve the same using Javascript possibly using a library like underscore?

Best Regards,

Carlskii

javascript
ruby
node.js
underscore.js

Answer 1

Just loop over the values and increment a count in a hash.

var count = {};
domains.forEach(function (obj) { 
    var c = obj.country;
    count[c] = count[c] ? count[c] + 1 : 1;
});

(Note that IE 8 and earlier don't support forEach, use a polyfill or a regular for loop if you care about them)

Answer 2

You can also use the reduce function much like in Ruby:

domains.reduce(function(country_with_count, country_object) {
    country_with_count[country_object['country']] = (country_with_count[country_object['country']] || 0) + 1;
    return country_with_count;
}, {});