filter an array of object based on a key and get only key value

Question

I want to filter an array of objects based on a key selected. If any of the object has selected: true, I want its ID in return. For e.g. below:

Below is the array I have:

arr = [
 {
    "_id": "6311eb86cc42295428bb663a",
    "name": "Southeast Asia",
    "language": [
        "English"
    ],
    "selected": true
 },
 {
    "_id": "6311eb86cc42295428bb663f",
    "name": "USA",
    "language": [
        "English"
    ],
 },
 {
    "_id": "6311eb86cc42295428bb6635",
    "name": "MENA",
    "language": [
        "English"
    ],
    "selected": true
 }
]

Logic used to get an _id from it:

arr.filter(item => {
   if(item.selected) {
     retrun item._id;
   }
});

Expected output:

[{
  _id: '6311eb86cc42295428bb663a'
}, {
  _id: '6311eb86cc42295428bb6635'
}]

But I got the whole array of object in return instead of just _id.

How can I work around this to get only _id?

mickl · Accepted Answer · 2022-10-06 10:12:51Z

3

The array.filter method only filters the input array without changing it's content. The callback you're passing in your code is only expected to return true or false. To reshape your result you need to use filter along with array.map

const arr = [
 {
    "_id": "6311eb86cc42295428bb663a",
    "name": "Southeast Asia",
    "language": [
        "English"
    ],
    "selected": true
 },
 {
    "_id": "6311eb86cc42295428bb663f",
    "name": "USA",
    "language": [
        "English"
    ],
 },
 {
    "_id": "6311eb86cc42295428bb6635",
    "name": "MENA",
    "language": [
        "English"
    ],
    "selected": true
 }
];

const result = arr.filter(item => item.selected).map(item => ({_id: item._id}));

console.log(result);

answered Oct 6, 2022 at 10:12

mickl

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Comments

flyingfox · Accepted Answer · 2022-10-06 10:13:11Z

1

const data = arr = [
 {
    "_id": "6311eb86cc42295428bb663a",
    "name": "Southeast Asia",
    "language": [
        "English"
    ],
    "selected": true
 },
 {
    "_id": "6311eb86cc42295428bb663f",
    "name": "USA",
    "language": [
        "English"
    ],
 },
 {
    "_id": "6311eb86cc42295428bb6635",
    "name": "MENA",
    "language": [
        "English"
    ],
    "selected": true
 }
]

let result = data.filter(d => d.selected).map(d => {
      let obj ={}
      obj['_id'] = d._id
      return obj
})
console.log(result)

answered Oct 6, 2022 at 10:13

flyingfox

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Comments

Hamza Dabaghi · Accepted Answer · 2022-10-06 10:21:22Z

1

You can use map as below :

let filtered = arr.filter(item => { if(item.selected) { return item._id;}}).map(item => ({_id: item._id}));;

expected output :

 [ { _id: '6311eb86cc42295428bb663a'}, { _id: '6311eb86cc42295428bb6635'}]

edited Oct 6, 2022 at 10:21

answered Oct 6, 2022 at 10:18

Hamza Dabaghi

113 bronze badges

1 Comment

Dawid Wekwejt Over a year ago

Use special code formating

Schulze · Accepted Answer · 2022-10-06 10:17:07Z

0

Array.filter returns an array based on your function.

So you have to save that variable like this:

let arr2= arr.filter(element => {
    if(element.selected == true)
        return (element)
});

answered Oct 6, 2022 at 10:17

Schulze

1087 bronze badges

Comments

Ka Sen Low · Accepted Answer · 2022-10-06 10:19:47Z

0

You need to use both filtered and map functions

const filteredArr = arr.filter((element)=>{
    return element.selected != null
})

const reducedArr = filteredArr.map((element) => {
    return {_id:element._id}
})

answered Oct 6, 2022 at 10:19

Ka Sen Low

11 bronze badge

Comments

MagicKriss · Accepted Answer · 2022-10-06 11:19:51Z

0

filter + map == reduce

so this will give you your output:

arr.reduce((acc,val)=>{
  if(val.selected){
    acc.push({_id: val._id})
  }
  return acc
},[])

Or, most likely you actually need just array of values:

arr.reduce((acc,val)=>{
  if(val.selected){
    acc.push(val._id)
  }
  return acc
},[])

answered Oct 6, 2022 at 11:19

MagicKriss

17816 bronze badges

2 Comments

MagicKriss Over a year ago

You can read about reduce here developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…

MagicKriss Over a year ago

Also, reduce will have 1 iteration instead of 2 in case of filter+map

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