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

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 ?

CodePudding user response：

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);

CodePudding user response：

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)

CodePudding user response：

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) {
  return {
    "AREA": [...prev["AREA"], ...curr["AREA"]],
    "SUPER_REGION": [...prev["SUPER_REGION"], ...curr["SUPER_REGION"]],
  };
}

let sum = finalVal.reduce(collecItems);

console.log(sum);