how to count keys present in array of object in javascript?

Question

I have an below array. I wanted to know how many time selectedOption key is present in array of Object. In, some object we don't have key selectedOption. So, the count of key selectedOption should return 4. How we can count these key in javascript ?

let data = [{
  id: 123,
  selectedOption: "ABC",
  value: 345
}, {
  id: 234,
  selectedOption: "BCD",
  value: 345
}, {
  id: 356,
  selectedOption: "BGY",
  value: 678
}, {
  id: 456,
  selectedOption: "BCD",
  value: 890
}, {
  id: 870: value: 980
}, {
  id: 385,
  value: 654
}]

What have you tried so far to solve this on your own? A simple loop with an if (typeof ...) should do the job. — Andreas
– Andreas, Commented Jun 13, 2020 at 12:02

Nicky McCurdy · Accepted Answer · 2020-06-13 12:01:03Z

6

data.filter(datum => datum.selectedOption).length

answered Jun 13, 2020 at 12:01

Nicky McCurdy

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Comments

hendrixchord · Accepted Answer · 2020-06-14 09:28:00Z

1

data.filter(d => d.hasOwnProperty('selectedOption')).length

This is a more full proof solution compared to data.filter(datum => datum.selectedOption).length because if selectedOption was a boolean flag with false value it wouldn't be counted.

hasOwnProperty will check if the property exists on the object irrespective of the value.

For example in this case

let data = [{
  id: 123,
  selectedOption: false,
  value: 345
}, {
  id: 234,
  selectedOption: false,
  value: 345
}, {
  id: 356,
  selectedOption: true,
  value: 678
}, {
  id: 456,
  selectedOption: false,
  value: 890
}, {
  id: 870,
  value: 980
}, {
  id: 385,
  value: 654
}];

data.filter(d => d.hasOwnProperty('selectedOption')).length Output: 4
data.filter(datum => datum.selectedOption).length Output: 1

edited Jun 14, 2020 at 9:28

answered Jun 13, 2020 at 12:04

hendrixchord

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2 Comments

β.εηοιτ.βε Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.

hendrixchord Over a year ago

@β.εηοιτ.βε thanks for the suggestion, I've added an explanation.

brk · Accepted Answer · 2020-06-13 12:03:17Z

0

There are multiple ways it can be done. In the below function ,reduce is used. Inside reduce callback it is checking if the object has selectedOption key then increment 1

let data = [{
  id: 123,
  selectedOption: "ABC",
  value: 345
}, {
  id: 234,
  selectedOption: "BCD",
  value: 345
}, {
  id: 356,
  selectedOption: "BGY",
  value: 678
}, {
  id: 456,
  selectedOption: "BCD",
  value: 890
}, {
  id: 870,
  value: 980
}, {
  id: 385,
  value: 654
}];

let countSelectedOption = data.reduce((acc, curr) => {
  acc += curr.selectedOption ? 1 : 0;
  return acc;
}, 0);
console.log(countSelectedOption)

answered Jun 13, 2020 at 12:03

brk

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