JavaScript Map Two arrays into in Multidimensional Object

Question

I need to take two arrays of separate arrays of objects and map it to a new array of objects. I just can't seem to figure it out in ES6. I know I need to map through the first array and reduce on the second array but I am getting lost. I included a snippet, which fails on the reduce at Combined: acc[i].Combined.push(name.SId),

two arrays:

Array 1

[
    {
      "BId": 1,
      "Name": "Test1",
    },
    {
      "BId": 2,
      "Name": "Test2",
    }
]

Array 2

[
    {
      "Id": 1,
      "BId": 1,
      "SId": 2,
      "GId": 1
    },
    {
      "Id": 2,
      "BId": 1,
      "SId": 2,
      "GId": 2
    },
    {
      "Id": 3,
      "BId": 1,
      "SId": 3,
      "GId": 1
    },
    {
      "Id": 1,
      "BId": 2,
      "SId": 2,
      "GId": 1
    },
    {
      "Id": 2,
      "BId": 2,
      "SId": 2,
      "GId": 2
    },
    {
      "Id": 3,
      "BId": 2,
      "SId": 3,
      "GId": 1
    },
    {
      "Id": 3,
      "BId": 2,
      "SId": 3,
      "GId": 4
    },
]

result:

[
    {
      "BId": 1,
      "Name": Test1,
      "Combined": [{SId:2, GIds[1,2]}, {SId:3, GIds[1]}]
    }
    {
      "BId": 2,
      "Name": Test2,
      "Combined": [{SId:2, GIds[1,2]}, {SId:3, GIds[1,4]}]
    }
]

const array1 = [
        {"BId": 1,
          "Name": "Test1",
        },
        {
          "BId": 2,
          "Name": "Test2",
        }
    ];
    
const array2 = [
        {
          "Id": 1,
          "BId": 1,
          "SId": 2,
		  "GId": 1
        },
        {
          "Id": 2,
          "BId": 1,
          "SId": 2,
		  "GId": 2
        },
        {
          "Id": 3,
          "BId": 1,
          "SId": 3,
		  "GId": 1
        },
		{
          "Id": 1,
          "BId": 2,
          "SId": 2,
		  "GId": 1
        },
        {
          "Id": 2,
          "BId": 2,
          "SId": 2,
		  "GId": 2
        },
        {
          "Id": 3,
          "BId": 2,
          "SId": 3,
		  "GId": 1
        },
        {
          "Id": 3,
          "BId": 2,
          "SId": 3,
		  "GId": 4
        },
    ];
    
    
     const all = array1.map(a1 => {
      combined = array2
        .filter(a2 => a2.BId === a1.BId)
        .reduce((acc, name, i) => {

          const obj = {
            BId: name.BId,
            Name: name.Name,
            Combined: acc[i].Combined.push(name.SId),
          };
          acc.push(obj);

          return acc;
        }, []);
      return bv;
    });

radulle · Accepted Answer · 2020-05-22 19:44:11Z

1

Hope it helps...

const array1 = [
        {"BId": 1,
          "Name": "Test1",
        },
        {
          "BId": 2,
          "Name": "Test2",
        }
    ];
    
const array2 = [
        {
          "Id": 1,
          "BId": 1,
          "SId": 2,
		  "GId": 1
        },
        {
          "Id": 2,
          "BId": 1,
          "SId": 2,
		  "GId": 2
        },
        {
          "Id": 3,
          "BId": 1,
          "SId": 3,
		  "GId": 1
        },
		{
          "Id": 1,
          "BId": 2,
          "SId": 2,
		  "GId": 1
        },
        {
          "Id": 2,
          "BId": 2,
          "SId": 2,
		  "GId": 2
        },
        {
          "Id": 3,
          "BId": 2,
          "SId": 3,
		  "GId": 1
        },
        {
          "Id": 3,
          "BId": 2,
          "SId": 3,
		  "GId": 4
        },
    ];
            
const all = array1.map(arr => {
  let combined = []
  array2
  .filter(e => arr.BId === e.BId)
  .forEach(e => {
    const {GId, SId} = e
    combined.push({GId, SId})
  })
  combined = combined.reduce((acc, cur) => {
  const {GId, SId} = cur
  const idx = acc.findIndex(e => e.SId === SId)
  if (idx !== -1) {acc[idx].GId.push(GId)}
  else {acc.push({SId, GId: [GId]})}
  return acc
  },[])
  return {...arr, combined}
 });
 
 console.log(all)

edited May 22, 2020 at 19:44

answered May 22, 2020 at 19:17

radulle

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6 Comments

Harleyz Over a year ago

Thanks for the quick response, but the result is not combined how it was stated, this is a lot closer than I got tho! GIds need to be combined within the combined object as well (thats the tricky part)

radulle Over a year ago

Ok, do I understand correctly that you want to aggregate based on SIds?

Harleyz Over a year ago

exactly, they group on SIds! :)

Harleyz Over a year ago

sweet. I am going to see if I can clean that up into ES6, but thats an aswer. Cheers mate.

radulle Over a year ago

@Harleyz You can't get more ES6 than this :D

|

Dananjaya Ariyasena · Accepted Answer · 2020-05-22 19:55:39Z

1

let a_array = [
    {
      "BId": 1,
      "Name": "Test1",
    },
    {
      "BId": 2,
      "Name": "Test2",
    }
];

let b_array = [
    {
      "Id": 1,
      "BId": 1,
      "SId": 2,
      "GId": 1
    },
    {
      "Id": 2,
      "BId": 1,
      "SId": 2,
      "GId": 2
    },
    {
      "Id": 3,
      "BId": 1,
      "SId": 3,
      "GId": 1
    },
    {
      "Id": 1,
      "BId": 2,
      "SId": 2,
      "GId": 1
    },
    {
      "Id": 2,
      "BId": 2,
      "SId": 2,
      "GId": 2
    },
    {
      "Id": 3,
      "BId": 2,
      "SId": 3,
      "GId": 1
    },
    {
      "Id": 3,
      "BId": 2,
      "SId": 3,
      "GId": 4
    },
];

a_array.map( (a_object) => {
 if(!a_object.Combined) a_object.Combined = [];

 return b_array.map((b_object) => {

  if(a_object.BId === b_object.BId) {

   let c = a_object.Combined.filter( (_c) => ( _c.SId === b_object.SId ) );

   if(c && c[0]) {
    if(!c[0].GIds.includes(b_object.GId)) c[0].GIds.push(b_object.GId);

   } else {
    a_object.Combined.push({"SId": b_object.SId, "GIds": [b_object.GId]})

   }

   return a_object;

  }

 })

} )

console.log(a_array);

edited May 22, 2020 at 19:55

answered May 22, 2020 at 19:48

Dananjaya Ariyasena

6063 silver badges16 bronze badges

2 Comments

Scott Sauyet Over a year ago

This feels like a bizarre use of map. Using map to update a value is strange enough, but using it to occasionally update it (depending upon some criteria) seems scary!

Harleyz Over a year ago

@ScottSauyet - i think filter would be okay here in place of the if(a_object.BId === b_object.BId). I will include the final result probably by end of day.

Scott Sauyet · Accepted Answer · 2020-05-23 11:59:44Z

I might write something like this:

const combine = (arr1, arr2) => arr1 .map (({BId, ...rest}) => ({
  BId, 
  ...rest,
  Combined: Object .entries (
      arr2 .filter (({BId: b}) => b == BId)
           .map (({SId, GId}) => ({SId, GId}))
           .reduce ((a, {SId, GId}) => ({...a, [SId]: [...(a [SId] || []), GId]}), {})
  ) .map (([sid, GIds]) => ({SId: Number (sid), GIds}))
}))


const arr1 = [{BId: 1, Name: "Test1"}, {BId: 2, Name: "Test2"}]
const arr2 = [{Id: 1, BId: 1, SId: 2, GId: 1}, {Id: 2, BId: 1, SId: 2, GId: 2}, {Id: 3, BId: 1, SId: 3, GId: 1}, {Id: 1, BId: 2, SId: 2, GId: 1}, {Id: 2, BId: 2, SId: 2, GId: 2}, {Id: 3, BId: 2, SId: 3, GId: 1}, {Id: 3, BId: 2, SId: 3, GId: 4}]


console .log (combine (arr1, arr2))

.as-console-wrapper {min-height: 100% !important; top: 0}

I think it's fairly straightforward. The BId and Name properties are taken from the first array (using ...rest to include other properties if they are there.) And we calculate Combined like this:

The filter line finds the matching entries.
The first map line extracts the two properties we care about.
The reduce line groups them into a structure like {"2": [1, 2], "3": [1]}.
We call Object.entries on that to get back [["2", [1, 2]], ["3", [1]]].
And then the second map line turns that into [{SId: 2, GIds: [1, 2]}, {SId: 3, GIds: [1]}). Because we used the SId as a key, it was turned into a String. We use Number here to convert it back.

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