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akko
Asked: 2020-08-16 08:04:29 +0800 CST 2020-08-16 08:04:29 +0800 CST

How could I count in a JSON array?

  • 772

Assuming I have an array of JSON that looks like this:

[
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': false
  },
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': true
  }
]

How could I count elements whose key asistio === true?

javascript

4 Answers

  1. Best Answer

    It can .filteralso be used, which makes it a bit shorter, since we can take advantage of the fact that it asistiois true or false :

    var arr = [{
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': false
  },
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': true
  }
]

var cant = arr.filter(o => o.asistio).length;

console.log(cant)

    • 12

  2. You just have to iterate through the array and count like this:

    var data = [
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': false
  },
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': true
  }
];
var asistieron = 0;
data.forEach(function(dato) {
  if(dato.asistio) {
    asistieron++;
  }
});
console.log(asistieron);

    • 6

  3. I would use reduce:

    const n = date.reduce((acc, {asistio}) => 
  asistio === true
    ? acc + 1
    : acc;
), 0);
    • 1

  4. I tell you that you can also use map(), which when iterating returns a new array and will show you the result you expect; it's just a matter of looking at it

    We go through the array and in the attended key we verify with the triple sign =if its property is true; if so, we add one to the counter that must be declared outside, once the above is done with a console.logwe print it outside, we use a ifto compare > the value we want to find and if so, make the counter increase

    let data = [
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': false
  },
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': true
  }
]

contador = 0
data.map((dato) => {
  if(dato.asistio === true){
    contador += 1
    
  }
})
console.log(contador)

    I also tell you that as the value you are looking to count how many times these are boolean; it is enough with the syntax like data.assisted since by default it will search first for those values ​​that are true, you can also use the ifternary syntax that has its structure in this way: (variable) ? valorAfirmatvo : valorFalsoas follows

    let data = [
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': false
  },
  {
    'nombre': 'X',
    'asistio': true
  },
  {
    'nombre': 'X',
    'asistio': true
  }
]

contador = 0
data.map((dato) => {
  (dato.asistio) ? contador += 1 : 0
})
console.log(contador)

    For more information about the map() method as well as examples that give you more clarity on how it works, I leave you reference documentation

    • 0