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":[
            "saaa@aa.com",
            "aaa.aaa@gmail.com"
         ],
         "name":"Registration Report"             
      },
      {
         "id":"45s4dsf4qdgze5zef1z3e2f1zevcd5s6sdfsdfsdf",
         "dailyemails":[
         ],
         "name":"Presentation"             
      },
      {
         "id":"7d7cc642ca13cc4a998cad364dfe8e623fd95ae3",
         "dailyemails":[
            "saaa@ss.com"
         ],
         "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](http://stackoverflow.com/questions/4009756/how-to-count-string-occurrence-in-string)). — skobaljic, Apr 26 '17 at 15:03
Use `map` and `filter`, and then count the resulting length. — evolutionxbox, Apr 26 '17 at 15:19

score 2 · Answer 1 · answered Apr 26 '17 at 15:07

2

filter all empty values out

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

answered Apr 26 '17 at 15:07

Yury Tarabanko

44,270
9
84
98

Luke Kot-Zaniewski · Answer 2 · 2017-04-26T15:15:09.727

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":[
            "saaa@aa.com",
            "aaa.aaa@gmail.com"
         ],
         "name":"Registration Report"             
      },
      {
         "id":"45s4dsf4qdgze5zef1z3e2f1zevcd5s6sdfsdfsdf",
         "dailyemails":[
         ],
         "name":"Presentation"             
      },
      {
         "id":"7d7cc642ca13cc4a998cad364dfe8e623fd95ae3",
         "dailyemails":[
            "saaa@ss.com"
         ],
         "name":"Live Report"
      }

   ]
}

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

ibrahim mahrir · Accepted Answer · 2017-04-26T15:28:37.617

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 '17 at 15:28

answered Apr 26 '17 at 15:09

ibrahim mahrir

31,174
5
48
73

2

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 :) – axelduch Apr 26 '17 at 15:19
1

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 – Luke Kot-Zaniewski Apr 26 '17 at 15:22
1

@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). – ibrahim mahrir Apr 26 '17 at 15:23
1

@ibrahimmahrir yup that's why I suggested either a cast to a boolean (either 0 or 1), same with min(1, 555) – axelduch Apr 26 '17 at 15:24
@LucasKot-Zaniewski Good point! Switching the places of `1` and `0` fix the problem. – ibrahim mahrir Apr 26 '17 at 15:24
1

@ibrahimmahrir my comment was directed towards axelduch, my apologies. But I see what you mean now. – Luke Kot-Zaniewski Apr 26 '17 at 15:27
@LucasKot-Zaniewski Good coincidence. Oops! The first version is the correct one. OP said _non-empty_ not empty objects. – ibrahim mahrir Apr 26 '17 at 15:28
@axelduch with the casting part I now understand what you are saying. Although it would make it more concise I like ibrahim's method due to slightly better readability imo – Luke Kot-Zaniewski Apr 26 '17 at 15:32
@LucasKot-Zaniewski I can only agree to that – axelduch Apr 26 '17 at 15:33
@axelduch glad we came to a consensus :-) – Luke Kot-Zaniewski Apr 26 '17 at 15:38

score 2 · Answer 4 · answered Apr 26 '17 at 15:10

You need to make use of the Array filter method.

var obj = {
   "templates":[
      {
         "id":"2c1d99d9b6b2fb417601d24c10c9b041a7d6f37b",
         "dailyemails":[
            "saaa@aa.com",
            "aaa.aaa@gmail.com"
         ],
         "name":"Registration Report"             
      },
      {
         "id":"45s4dsf4qdgze5zef1z3e2f1zevcd5s6sdfsdfsdf",
         "dailyemails":[
         ],
         "name":"Presentation"             
      },
      {
         "id":"7d7cc642ca13cc4a998cad364dfe8e623fd95ae3",
         "dailyemails":[
            "saaa@ss.com"
         ],
         "name":"Live Report"
      }

   ]
};

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

javascript get count of non-empty JSON subarrays

4 Answers4