I'd like to count the number of items in an array of JSON items that match some conditions. My array look like this:

array = [{
            name: 'Bob',
            age: 24
           },
          ....,
          {
            name: 'Mary',
            age: 23
           }]

Rather than looping through the whole array I am trying to get an expression as simple an as elegant as my database request:

db.myCollection.find({ age: 23 }).count()

Is there any best practice? I was thinking of using the underscore library but I couldnt find what I am looking for.

Many thanks for your help.

I'd like to count the number of items in an array of JSON items that match some conditions. My array look like this:

array = [{
            name: 'Bob',
            age: 24
           },
          ....,
          {
            name: 'Mary',
            age: 23
           }]

Rather than looping through the whole array I am trying to get an expression as simple an as elegant as my database request:

db.myCollection.find({ age: 23 }).count()

Is there any best practice? I was thinking of using the underscore library but I couldnt find what I am looking for.

Many thanks for your help.

• javascript
• json
• angularjs

• Can you be a little clearer on what kind of conditions you are talking about? Is it just the existence of certain keys in the JSON object or are they actual conditions of certain keys being equal to certain values? – aug Commented Mar 25, 2014 at 21:46
• Isn't Array.prototype.filter() an option? developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… – jarandaf Commented Mar 25, 2014 at 21:46
• If you're using underscore there's _.size(..) – megawac Commented Mar 25, 2014 at 21:49

2 Answers 2

Well, you can do this without any 3rd party library and also without looping:

array.filter(function(value) { return value.age === 23 }).length;

And with ES6 it even becomes more terse

array.filter(value => value.age === 23).length;

As I mentioned in op, it seems like you're looking for _.size

_.chain(json)
 .find({age: 23})
 .size()
 .value();