How to combine an array of object within same array and same keys using reduce

Question

I am trying to combine objects inside an array using reduce my object looks like bellow and has the fallowing structure.

[
    {
        "AREA": [
            "EMAC"
        ],
        "SUPER_REGION": [
            "South East Europe Region",
            "East Europe Region",
        ],
    },
    {
        "AREA": [
            "CCA"
        ],
        "SUPER_REGION": [
            "Taiwan",
            "China Hong Kong"
        ],
    }
    
]

Expected output :

{
        "AREA": [
            "EMAC","CCA"
        ],
        "SUPER_REGION": [
            "South East Europe Region",
            "East Europe Region",
            "Taiwan",
            "China Hong Kong"
        ],
}

My current code using reduce :

let sum = finalval.reduce(function (accumulator, { AREA, SUPER_REGION }) {
    accumulator["AREA"] += AREA;
    return accumulator;
  }, {});

the above code returns me output by combining the values into one string but I want them to be split and added into a single object like shown in expected output. How can i actually push values into these object like we do on arrays using push method ?

CertainPerformance · Accepted Answer · 2022-12-05 05:55:02Z

You would need to append elements not only to AREA, but to SUPER_REGION as well - to add elements to an array, use .push, not +=. But that wouldn't be very general. A more flexible approach would construct the output object by first mapping one of the input objects, with empty arrays as values - then for each input object, iterate over each subarray and push to the key in the output object.

const input = [
    {
        "AREA": [
            "EMAC"
        ],
        "SUPER_REGION": [
            "South East Europe Region",
            "East Europe Region",
        ],
    },
    {
        "AREA": [
            "CCA"
        ],
        "SUPER_REGION": [
            "Taiwan",
            "China Hong Kong"
        ],
    }  
];

const output = Object.fromEntries(
  Object.keys(input[0]).map(key => [key, []])
);
for (const obj of input) {
  for (const [key, subarr] of Object.entries(obj)) {
    output[key].push(...subarr);
  }
}
console.log(output);

.reduce isn't really appropriate here, assuming you want to keep the input unmutated. If you have to use .reduce, it will look a bit confusing for no good reason.

const input = [{
    "AREA": [
      "EMAC"
    ],
    "SUPER_REGION": [
      "South East Europe Region",
      "East Europe Region",
    ],
  },
  {
    "AREA": [
      "CCA"
    ],
    "SUPER_REGION": [
      "Taiwan",
      "China Hong Kong"
    ],
  }
];

const output = input.reduce((a, obj) => {
  for (const [key, subarr] of Object.entries(obj)) {
    a[key].push(...subarr);
  }
  return a;
}, Object.fromEntries(Object.keys(input[0]).map(key => [key, []])));
console.log(output);

Andrew Parks · Accepted Answer · 2022-12-05 06:28:51Z

2

const d = [{"AREA":["EMAC"],"SUPER_REGION":["South East Europe Region","East Europe Region"]},{"AREA":["CCA"],"SUPER_REGION":["Taiwan","China Hong Kong"]}]

const r = d.reduce((a,c)=>(Object.keys(c).forEach(k=>a[k].push(...c[k])),a))

console.log(r)

answered Dec 5, 2022 at 6:28

Andrew Parks

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Comments

Rohìt Jíndal · Accepted Answer · 2022-12-05 06:42:52Z

0

You can achieve this requirement by using Array.reduce() method.

Live Demo :

const arr = [
  {
    "AREA": [
      "EMAC"
    ],
    "SUPER_REGION": [
      "South East Europe Region",
      "East Europe Region",
    ],
  },
  {
    "AREA": [
      "CCA"
    ],
    "SUPER_REGION": [
      "Taiwan",
      "China Hong Kong"
    ],
  }
];

const res = arr.reduce((obj, curr) => {
    Object.keys(curr).forEach(key => {
    obj[key] = obj[key] ? [...obj[key], ...curr[key]] : curr[key]
  })
  return obj
}, {});

console.log(res);

answered Dec 5, 2022 at 6:42

Rohìt Jíndal

27.4k16 gold badges80 silver badges133 bronze badges

Comments

blurfus · Accepted Answer · 2022-12-05 06:55:48Z

You could merge the arrays from all the objects in the input.

Something along the lines of the code below:

let finalVal = [{
    "AREA": [
      "EMAC"
    ],
    "SUPER_REGION": [
      "South East Europe Region",
      "East Europe Region",
    ],
  },
  {
    "AREA": [
      "CCA"
    ],
    "SUPER_REGION": [
      "Taiwan",
      "China Hong Kong"
    ],
  }
];


function collecItems(prev, curr) {
  // to make it more generic, get the keys from the first element in the array:
  let objectKeys = Object.keys(finalVal[0]);
  console.log(objectKeys);

  // build the object with the keys
  let rtnObj = {};

  objectKeys.forEach(key => {
    // add the values for each key
    rtnObj[key] = [...prev[key], ...curr[key]];
  });
  return rtnObj;
}

let sum = finalVal.reduce(collecItems);

console.log(sum);

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