Get the number of true/false values in an array using javascript

Question

I'm having an Array with properties id and value

 var arrayObj=  [
        {"id": 1, "value": true},
        {"id": 2, "value": false},
        {"id": 3, "value": true}
    ]

I need to get the number of objects that has the property true/false. I'm using Array.prototype.every() but my logic is not working as intended as it seems. Can anyone tell me what I'm doing wrong here? I'm not displaying the count

function checkIfFalse(value, index, ar) {
     document.write(value + " ");
     if (value  === false)
         return true;
     else
        return false;
}

if (arrayObj.every(checkIfFalse)) {
    console.log("all are false");
}else {
    console.log("all are true");
}

the logic doesn't make sense to me. not( all false) != all true — Paul
– Paul, Commented Aug 20, 2015 at 5:29

roland · Accepted Answer · 2020-06-24 07:45:07Z

11

Why not using .filter?

// Your array object
var arrayObj = [
  {"id": 1, "value": true},
  {"id": 2, "value": false},
  {"id": 3, "value": true}
];

// Count true items
var count = arrayObj.filter(function(s) { return s.value; }).length;

// Result
console.log("#True: " + count);

edited Jun 24, 2020 at 7:45

answered Sep 25, 2017 at 9:25

roland

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4 Comments

socca1157 Over a year ago

How can you use .filter to only find the false items?

roland Over a year ago

@socca1157 Just add "!" prior to s.value to invert the boolean. var count = arrayObj.filter(function(s) { return !s.value; }).length;

socca1157 Over a year ago

I tried that, but wouldn't let me compare against a false or null value. I ended up converting the var to a string and doing a direct comparison that way. Thanks!

roland Over a year ago

@socca1157 Really? That's weird. For me it works with false and null.

Scott Selby · Accepted Answer · 2015-08-20 05:37:54Z

the .every() function is expecting being passed an function which will test each item of the array and return true or false. you would want something like:

  if (arrayObj.every(checkIfFalse)) {
                console.log("all are false");
  }

 function checkIfFalse(value, index, ar) {
   console.log('checking if' + index + ' from array is false');
   return value.value == false;
 }

so, arrayObj.every(checkIfFalse) will return false , because not all items are false

.every() is used to check if EVERY item of an array meets a certain condition, it sounds like you want to get a count of the number of items which meet a certain condition. There is no way to do this without iterating through each item of the array and checking. Thhis will be best if you just write your own for loop. ex:

function countItemsTrue(arry){
   var result = 0;
   for(x = 1; arry.length >= x; x++){
      if(arry[x].value === true){
        result++;
      }
   }
   return result;

}

then you would do

  var count = CountItemsTrue(arrayObj);

when it's written like this you can easily check if all are true without iterating all over just by checking:

  var allTrue = count == arrayObj.length;

Paul · Accepted Answer · 2015-08-20 05:36:09Z

2

you can do like this

int falses=0,trues=0;
for(i=0;i<arrayObj.length;i++) {
    if(arrayObj[i].value) {
        trues++;
    } else {
        falses++;
    }
}
console.log('Trues: '+trues+' Falses:'+falses);

edited Aug 20, 2015 at 5:36

Paul

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answered Aug 20, 2015 at 5:29

Raghavendra

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Comments

Mac · Accepted Answer · 2015-08-20 05:56:13Z

2

I'm not entirely sure what you actually want: you state a number of times that you want to count how many items have false values, yet your discussion of the code makes it sound like you only want to know if they all have false value properties.

If it's the first that you're after (the actual number of false values), you can get that by using reduce as follows:

var arrayObj = [
    { "id": 1, "value": true },
    { "id": 2, "value": false },
    { "id": 3, "value": true }
];

var numFalse = arrayObj.reduce(function(count, item) {
    return count + (item["value"] === false ? 1 : 0);
}, 0);

If it's the second (you want to know if all values are false), or you want to check if none or only some of the entries have false value entries, you can achieve those as follows:

var allFalse = numFalse == data.length,
    noneFalse = numFalse == 0,
    someFalse = numFalse > 0 && numFalse < data.length;

If you're not familiar with reduce, it works like this:

The second parameter to reduce (a zero) sets the initial count to zero.
For each item in the array, the function passed to reduced is called, with the first value being the current count and the second being the current item in the array.
If the item's value property is false, we add one to the count, otherwise we add zero.
At the end, reduce returns the final value of the count.

edited Aug 20, 2015 at 5:56

answered Aug 20, 2015 at 5:40

Mac

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1 Comment

Scott Selby Over a year ago

I like this , as it's a nice elegent solution and will surely get poster in trouble if it happens to be homework instead of an actual problem

Teocci · Accepted Answer · 2020-08-29 09:20:24Z

2

var arrayObj = [{
  "id": 1,
  "value": true
}, {
  "id": 2,
  "value": false
}, {
  "id": 3,
  "value": true
}];

var trueCount = falseCount = 0;

arrayObj.forEach(function(object) {
  object.value === true ? trueCount++ : falseCount++;
});

console.log(trueCount, falseCount);

DEMO

edited Aug 29, 2020 at 9:20

Teocci

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answered Aug 20, 2015 at 5:32

Deepak Ingole

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Comments

Teocci · Accepted Answer · 2020-08-29 09:18:50Z

1

var arrayObj = [{
    "id": 1,
    "value": true
  },

  {
    "id": 2,
    "value": false
  },
  {
    "id": 3,
    "value": true
  }
];

Array.prototype.numBoolean = function(condition) {
  var counter = 0;

  for (var i = 0; i < this.length; i++) {
    if (this[i].value === condition) {
      counter++;
    }
  }
  return counter;
};

console.log(arrayObj.numBoolean(true));
console.log(arrayObj.numBoolean(false));

edited Aug 29, 2020 at 9:18

Teocci

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answered Aug 20, 2015 at 5:32

SuperVeetz

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Comments

Teocci · Accepted Answer · 2020-08-29 09:22:10Z

1

Do like this, use array.forEach instead of native iteration.

var arrayObj = [{
    "id": 1,
    "value": true
  },

  {
    "id": 2,
    "value": false
  },
  {
    "id": 3,
    "value": true
  }
];

var trueCount = 0,
  falseCount = 0;

arrayObj.forEach(function(index) {
  if (index.value == true) {
    trueCount++;
  } else if (index.value == false) {
    falseCount++;
  }
});

console.log('True Obj is ' + trueCount + ' False Obj is ' + falseCount);

edited Aug 29, 2020 at 9:22

Teocci

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answered Aug 20, 2015 at 5:50

napster

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