How to Filter Object out of nested Array

Question

I try to filter the hole Object (objB) out of an Array, which is matching a Value (titleB2) of a Property.

const array = [
  {
    name: 'objA',
    subArray: []
  }, {
    name: 'objB',
    subArray: [
      {
        title: 'titleB'
      }, {
        title: 'titleB2'
      }, {
        title: 'titleB3'
      }
    ]
  }, {
    name: 'objC',
    subArray: [
      {
        title: 'titleC'
      }, {
        title: 'titleC2'
      }, {
        title: 'titleC3'
      }
    ]
  }, {
    name: 'objD',
    subArray: []
  }
]

const filterArray = array.filter(a => a.subArray.length > 0);
console.log(filterArray);
// Output: objB + objC

const resArray = filterArray.filter(a => a.subArray.filter(f => f.title === 'titleB2'));
console.log(resArray);
// Output: objB + objC

I guess, I do something logically wrong. But what exactly?

I need the output

{
  name: 'objB',
  subArray: [
    {
      title: 'titleB'
    }, {
      title: 'titleB2'
    }, {
      title: 'titleB3'
    }
  ]
}

I can imagine I use the filter filterArray.filter() wrong, because it already filtered? But I do this because I have multiple arrays in one array. Well, I am not realy sure, to be honest.

But what I dont understand is, why can I use the condition a => a.subArray.length > 0? but not f => f.title === 'titleB2'

Mark · Accepted Answer · 2019-04-03 17:21:31Z

1

To find objects with a particular title in the subarray you can use some() on the subarray, which will return true if one of the items in the subarray matches your condition (in this case the title):

const array = [{name: 'objA',subArray: []}, {name: 'objB',subArray: [{title: 'titleB'}, {title: 'titleB2'}, {title: 'titleB3'}]}, {name: 'objC',subArray: [{title: 'titleC'}, {title: 'titleC2'}, {title: 'titleC3'}]}, {name: 'objD',subArray: []}]

let found = array.filter(item => item.subArray.some(sub => sub.title === 'titleB2'))
console.log(found)

answered Apr 3, 2019 at 17:21

Mark

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3 Comments

equaliser Over a year ago

Thank you very much! This really helped me

Mark Over a year ago

No need to thank people @equaliser — that's what upvotes and selecting the correct answer are for.

equaliser Over a year ago

I know, but I mustnt: "Thanks for the feedback! Votes cast by those with less than 15 reputation are recorded, but do not change the publicly displayed post score." Thats why i mention that, so you know that I am really thankful :)

charlietfl · Accepted Answer · 2019-04-03 17:22:02Z

0

Use some() instead of filter() on subarray. It returns a boolean.

const resArray = array.filter(a => a.subArray.some(f => f.title === 'titleB2'));
console.log(resArray);
// Output: objB + objC

<script>

const array = [
  {
    name: 'objA',
    subArray: []
  }, {
    name: 'objB',
    subArray: [
      {
        title: 'titleB'
      }, {
        title: 'titleB2'
      }, {
        title: 'titleB3'
      }
    ]
  }, {
    name: 'objC',
    subArray: [
      {
        title: 'titleC'
      }, {
        title: 'titleC2'
      }, {
        title: 'titleC3'
      }
    ]
  }, {
    name: 'objD',
    subArray: []
  }
]
</script>

answered Apr 3, 2019 at 17:22

charlietfl

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1 Comment

equaliser Over a year ago

wow, ok thanks that clears the thing out for me. Thank you very much! :D

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