Getting an array from array of array objects

Question

I have an array which consists of an array objects as shown:

dataArr = [
    {
       id: 1,
       arrObj: [
          {
             id: 11,
             label: 'apple'
          },
          {
             id: 12,
             label: 'ball'
          }
       ]
    },
    {
       id: 2,
       arrObj: [
          {
             id: 21,
             label: 'car'
          },
          {
             id: 22,
             label: 'dog'
          }
       ]
    }
];

I need to extract an array consisting of only arrObj objects:

var newArr = [
    {
         id: 11,
         label: 'apple'
      },
      {
         id: 12,
         label: 'ball'
      },
      {
         id: 21,
         label: 'car'
      },
      {
         id: 22,
         label: 'dog'
      }
];

Tried using reduce method unsuccessfully:

 dataArr.reduce((previousValue, currentValue, currentIndex, array) => {
     return previousValue. arrObj.concat(currentValue.arrObj)
 });

Let me know how to do this. Thanks

Alan Omar · Accepted Answer · 2021-09-16 18:52:33Z

6

let dataArr = [
    {
       id: 1,
       arrObj: [
          {
             id: 11,
             label: 'apple'
          },
          {
             id: 12,
             label: 'ball'
          }
       ]
    },
    {
       id: 2,
       arrObj: [
          {
             id: 21,
             label: 'car'
          },
          {
             id: 22,
             label: 'dog'
          }
       ]
    }
];

let result = dataArr.flatMap(e => e.arrObj)
console.log(result)

answered Sep 16, 2021 at 18:52

Alan Omar

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Comments

Barmar · Accepted Answer · 2021-09-16 18:54:03Z

2

You were pretty close.

There's no arrObj property in your result, it's just an array.
You need to provide an empty array as the initial value argument to reduce().

const dataArr = [{
    id: 1,
    arrObj: [{
        id: 11,
        label: 'apple'
      },
      {
        id: 12,
        label: 'ball'
      }
    ]
  },
  {
    id: 2,
    arrObj: [{
        id: 21,
        label: 'car'
      },
      {
        id: 22,
        label: 'dog'
      }
    ]
  }
];

const newArr = dataArr.reduce((previousValue, currentValue) => {
  return previousValue.concat(currentValue.arrObj)
}, []);

console.log(newArr);

answered Sep 16, 2021 at 18:54

Barmar

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1 Comment

Barmar Over a year ago

The flatMap solution is probably better.

TAHER El Mehdi · Accepted Answer · 2021-09-16 19:11:56Z

0

You could use in one line by using Spread Operator...

dataArr.reduce((previousValue, currentValue) => [...previousValue?.arrObj, ...currentValue?.arrObj]);

Tip: use Optional chaining ?. in case there is no property arrObj!

answered Sep 16, 2021 at 19:11

TAHER El Mehdi

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Comments

PeterKA · Accepted Answer · 2021-09-16 19:47:48Z

0

You can use the Array#reduce method as follows:

let dataArr = [
    {
       id: 1,
       arrObj: [
          {
             id: 11,
             label: 'apple'
          },
          {
             id: 12,
             label: 'ball'
          }
       ]
    },
    {
       id: 2,
       arrObj: [
          {
             id: 21,
             label: 'car'
          },
          {
             id: 22,
             label: 'dog'
          }
       ]
    }
];

let newArr = dataArr.reduce((acc,cur) => [...acc, ...cur.arrObj], []);

console.log( newArr );

edited Sep 16, 2021 at 19:47

answered Sep 16, 2021 at 19:38

PeterKA

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