javascript get count of non-empty JSON subarrays

Question

How can I count the number of non-empty dailyemails in the following json?

{
   "templates":[
      {
         "id":"2c1d99d9b6b2fb417601d24c10c9b041a7d6f37b",
         "dailyemails":[
            "[email protected]",
            "[email protected]"
         ],
         "name":"Registration Report"             
      },
      {
         "id":"45s4dsf4qdgze5zef1z3e2f1zevcd5s6sdfsdfsdf",
         "dailyemails":[
         ],
         "name":"Presentation"             
      },
      {
         "id":"7d7cc642ca13cc4a998cad364dfe8e623fd95ae3",
         "dailyemails":[
            "[email protected]"
         ],
         "name":"Live Report"
      }

   ]
}

I am currently reading the total number of nodes Object.keys(myArr).length:

function metaInfo (id, cb){

    var URL = someURLhere
    var count = []

    fs.readFile(__dirname +'/' + URL+'/myFile.json', 'utf8', function   (err, data) {
        if (err) cb (err);
        obj = JSON.parse(data);
        var myArr = obj.nodes;
        count.push(Object.keys(myArr).length);
        cb(null, count)
    });
};

How can I read the number of non-empty dailyemails?

Probably to loop and count, but if your json is compressed, than you could look for and count "dailyemails":[] - it may speed up the process (method here). — skobaljic
– skobaljic, Commented Apr 26, 2017 at 15:03
Use map and filter, and then count the resulting length. — evolutionxbox
– evolutionxbox, Commented Apr 26, 2017 at 15:19

ibrahim mahrir · Accepted Answer · 2017-04-26 15:28:37Z

2

You can use reduce like this:

var count = myArray.reduce(function(c, o) {
    return c + (o.dailyemails.length? 1: 0);
}, 0);

even shorter using arrow functions:

var count = myArray.reduce((c, o) => c + (o.dailyemails.length? 1: 0), 0);

edited Apr 26, 2017 at 15:28

answered Apr 26, 2017 at 15:09

ibrahim mahrir

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10 Comments

a-d Over a year ago

You don't actually need a ternary for the short version, unary operator + expression in this case will always return a number, if you use !!. You could also use Math.min(1, o.dailyemails.length). Upvoted btw :)

Luke Kot-Zaniewski Over a year ago

yea but then we would be aggregating the lengths of the non empty arrays and not the number of non-empty arrays which is what we want

ibrahim mahrir Over a year ago

@axelduch The ternary is to check whether or not the array is empty. If I take it off then ther could be some undesired result (if the array length is 555 for example).

a-d Over a year ago

@ibrahimmahrir yup that's why I suggested either a cast to a boolean (either 0 or 1), same with min(1, 555)

Luke Kot-Zaniewski Over a year ago

@ibrahimmahrir my comment was directed towards axelduch, my apologies. But I see what you mean now.

|

Yury Tarabanko · Accepted Answer · 2017-04-26 15:07:20Z

2

filter all empty values out

var count = obj.templates.filter(item => item.dailyemails.length).length

answered Apr 26, 2017 at 15:07

Yury Tarabanko

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Comments

Abhinav Galodha · Accepted Answer · 2017-04-26 15:10:29Z

You need to make use of the Array filter method.

var obj = {
   "templates":[
      {
         "id":"2c1d99d9b6b2fb417601d24c10c9b041a7d6f37b",
         "dailyemails":[
            "[email protected]",
            "[email protected]"
         ],
         "name":"Registration Report"             
      },
      {
         "id":"45s4dsf4qdgze5zef1z3e2f1zevcd5s6sdfsdfsdf",
         "dailyemails":[
         ],
         "name":"Presentation"             
      },
      {
         "id":"7d7cc642ca13cc4a998cad364dfe8e623fd95ae3",
         "dailyemails":[
            "[email protected]"
         ],
         "name":"Live Report"
      }

   ]
};

var nonEmptyDailyEmails = obj.templates.filter(x => x.dailyemails && x.dailyemails.length > 0);
var countOfnonEmptyDailyEmails = nonEmptyDailyEmails.length;
console.log(countOfnonEmptyDailyEmails);

Luke Kot-Zaniewski · Accepted Answer · 2017-04-26 15:15:09Z

Instead of creating an array with filter and then getting the length you can also use reduce. This doesn't have the same overhead as filter because the only thing you are storing is the counter in the temporary variable p.

var x = {
   "templates":[
      {
         "id":"2c1d99d9b6b2fb417601d24c10c9b041a7d6f37b",
         "dailyemails":[
            "[email protected]",
            "[email protected]"
         ],
         "name":"Registration Report"             
      },
      {
         "id":"45s4dsf4qdgze5zef1z3e2f1zevcd5s6sdfsdfsdf",
         "dailyemails":[
         ],
         "name":"Presentation"             
      },
      {
         "id":"7d7cc642ca13cc4a998cad364dfe8e623fd95ae3",
         "dailyemails":[
            "[email protected]"
         ],
         "name":"Live Report"
      }

   ]
}

alert(x["templates"].reduce(function(p, e)
              {
                if(e["dailyemails"].length !==0)
                    p+=1;
                return p;
              },0));

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