Collect Array elements under array if one of the key is same

Question

I have an array collecting objects like

myArray = [ 
           { lid_id: "1_1", et: "car", ty: "STS", dc: null, c: null, cp: null, im: false},
           { lid_id: "1_1", et: "car", ty: "STS", dc: 7, c: 11333, cp: 60, im: true},
           { lid_id: "1_2", et: "car", ty: "STC", dc: null, c: null, cp: null, im: false},
           { lid_id: "10_14473", et: "truck", ty: null, dc: 7, c: 14869, cp: 40, im: true}
          ]

I want to build new objects and colllect dc, c, cp and im keys if lid_id has the same value. For example following object which has key-value "lid_id":"1_1" collects the elements under ce. How can I collect these elements if lid_id is same?

myArray.forEach(function(data){
    "body": { "lid_id": "1_1",
              "et": "car", 
              "ty": "STS",
              "ce": [ 
                      { 
                        "dc": null, 
                        "c": null, 
                        "cp": null, 
                        "im": false
                      },
                      {
                        "dc": 7, 
                        "c": 11333, 
                        "cp": 60, 
                        "im": true
                      } 
                    ]
            },
     "body": { "lid_id": "1_2",
              "et": "car", 
              "ty": "STC",
              "ce": [ 
                      { 
                        "dc": null, 
                        "c": null, 
                        "cp": null, 
                        "im": false
                      }
                    ]
            },
     "body": { "lid_id": "10_14473",
               ...............
             }
})

As far as I understand the expected result, the structure you are proposing does not work, because there cant be multiple "body": { ... }" entries on the same level. — Samuel Kirschner
– Samuel Kirschner, Commented Sep 19, 2018 at 12:07

deerawan · Accepted Answer · 2018-09-19 12:17:28Z

My method is using reduce to achieve the output.

const myArray = [{
    lid_id: "1_1",
    et: "car",
    ty: "STS",
    dc: null,
    c: null,
    cp: null,
    im: false
  },
  {
    lid_id: "1_1",
    et: "car",
    ty: "STS",
    dc: 7,
    c: 11333,
    cp: 60,
    im: true
  },
  {
    lid_id: "1_2",
    et: "car",
    ty: "STC",
    dc: null,
    c: null,
    cp: null,
    im: false
  },
  {
    lid_id: "10_14473",
    et: "truck",
    ty: null,
    dc: 7,
    c: 14869,
    cp: 40,
    im: true
  }
];

const grouping = myArray.reduce((acc, curr) => {
  const foundIndex = acc.findIndex(a => a.lid_id === curr.lid_id);
  const {
    dc,
    c,
    cp,
    im,
    lid_id,
    et,
    ty
  } = curr;
  const ceItem = {
    dc,
    c,
    cp,
    im
  };
  
  if (foundIndex > -1) {
    acc[foundIndex].ce.push(ceItem);
    return acc;
  }

  return [
    ...acc,
    {
      lid_id,
      et,
      ty,
      ce: [
        ceItem
      ]
    }
  ]
}, []);

console.log(grouping);

Μenelaοs · Accepted Answer · 2018-09-19 12:11:58Z

The first step is to pre-filter the data by the ID into a map containing an array of sub entries:

let myArray = [ 
           { lid_id: "1_1", et: "car", ty: "STS", dc: null, c: null, cp: null, im: false},
           { lid_id: "1_1", et: "car", ty: "STS", dc: 7, c: 11333, cp: 60, im: true},
           { lid_id: "1_2", et: "car", ty: "STC", dc: null, c: null, cp: null, im: false},
           { lid_id: "10_14473", et: "truck", ty: null, dc: 7, c: 14869, cp: 40, im: true}
          ];

console.log(myArray);

let myMap = [[]];

myArray.forEach( e =>
    {
            let internalArray = myMap[e.lid_id];
      console.log("internal: " + internalArray);

      if(internalArray == undefined){
         myMap[e.lid_id] = [];      
      }

            myMap[e.lid_id].push(e);

    }
);

console.log(myMap);

After that, it's just simple to do some further processing in order to get the appropriate groupings.

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