combining duplicate key's values in JavaScript array

Question

I have an Array that contain some keys/values one of the values is an array I want combining the value of array from all recorded that have same key in my Array.

Below is an Simple Example to demonstrate, I am not able to construct its logic so seeking help in building a logic to it.

[{"somekey":"Some Value Pushed"},{"somekey":"Second Value"}]

I want Result Like,

[{"somekey":["Some Value Pushed","Second Value"]}]

Does this answer your question? [Most efficient method to groupby on an array of objects](https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects) — pilchard, May 15 '21 at 19:15
Downvoted because of lack of clarity and lack of response to the answers given. The only answer that has been upvoted doesn't even return an array as required. Please add some more objects with different keys to your Array and Result so your requirements are comprehensible. — MikeM, May 17 '21 at 20:01

Reinis · Answer 1 · 2021-05-17T20:59:23.673

The reduce() function of Array Object in JavaScript can merge any array into a single Object. I wrote a single-line code to solve this problem. I updated result with the array.

 const arr = [{
        somekey: "Some Value Pushed",
      },
      {
        somekey2: "Second Value2",
      },
      {
        somekey: "Some Value Pushed",
      },
      {
        somekey2: "Second Value3",
      },
      {
        somekey3: "",
      },
      {},
    ];

    const ansObj = arr.reduce(
      (prv, cur) => {
        Object.entries(cur).forEach(([key, v]) => key in prv ? prv[key].push(v) : (prv[key] = [v]));
        return prv;
      }, {}
    )
    const ansArray = Object.entries(ansObj).map(([key, value])=>({[key]:value}));
    

    console.log(ansArray);

Doesn't return an array as is required. – MikeM May 17 '21 at 20:03 — MikeM, May 17 '21 at 20:03

score 0 · Answer 2 · answered May 15 '21 at 18:28

You can try something like this:

var array = [{
  name: "foo1",
  value: "val1"
}, {
  name: "foo1",
  value: ["val2", "val3"]
}, {
  name: "foo2",
  value: "val4"
}];

var output = [];

array.forEach(function(item) {
  var existing = output.filter(function(v, i) {
    return v.name === item.name;
  });
  if (existing.length) {
    var existingIndex = output.indexOf(existing[0]);
    output[existingIndex].value = output[existingIndex].value.concat(item.value);
  } else {
    if (typeof item.value === 'string')
      item.value = [item.value];
    output.push(item);
  }
});

Or, another option using Lodash

function mergeNames (arr) {
    return _.chain(arr).groupBy('name').mapValues(function (v) {
        return _.chain(v).pluck('value').flattenDeep();
    }).value();
}

score 0 · Answer 3 · answered May 15 '21 at 18:39

Maybe something like:

const data = [
  {"somekey":"Some Value Pushed"},
  {"somekey":"Second Value", "otherkey": 1},
  {"otherkey": 2}
];

const merge_and_group = (obj1, obj2) =>
  Object.entries(obj2).reduce(
    (acc, [key, val]) => {
      acc[key] ??= [];
      acc[key].push(val);
      return acc;
    },
    obj1
  );

const res = data.reduce(merge_and_group, {});

console.log(res);

score 0 · Answer 4 · answered May 15 '21 at 18:40

const arr = [{
  "somekey": "Some Value Pushed"
}, {
  "somekey2": "Second Value2"
}, {
  "somekey": "Some Value Pushed"
}, {
  "somekey2": "Second Value3"
}]

const newarr = {}
arr.forEach(obj => {
  for (const [key, value] of Object.entries(obj)) {
    if (newarr[key]) newarr[key].push(value)
    else newarr[key] = [value]
  }
})

console.log(newarr)

score 0 · Answer 5 · answered May 15 '21 at 18:41

Array.prototype.reduce() is a possible option.

the reduce() method executes a reducer function which is provided as an input on each element of the array and returning a single output value.

const array = [{"somekey":"Some Value Pushed"},{"somekey":"Second Value"}];

const res = array.reduce((acc, el) => {
  const [key, value] = Object.entries(el)[0];
  (acc[key] || (acc[key] = [])).push(value);
  return acc;
}, {});

console.log(res)

score 0 · Answer 6 · answered May 15 '21 at 19:59

Assuming each element of your array is an object with a single key.

const array = [
  { somekey: "Some Value Pushed" },
  { somekey: "Second Value" },
  { foo: "bar" },
  { foo: "baz" },
  { somekey: "Third Value" },
];

const result = [];

array.forEach(el => {
  let [key, value] = Object.entries(el)[0];
  for (let el of result) if (key in el) {
    el[key].push(value);
    return;
  } 
  result.push({ [key]: [value] });
});

console.dir(result);

score 0 · Answer 7 · answered May 15 '21 at 20:54

0

If your array has only "somekey" as keys then you can use map method as following:

const array = [{"somekey":"Some Value Pushed"},{"somekey":"Second Value"}];

const valuesArray = array.map(obj => obj.somekey);

result = [{"somekey":valuesArray}];

console.log(result)

answered May 15 '21 at 20:54

M. Saudagar

1
1
1

If there are other keys along with "somekey" then use filter() before using map() – M. Saudagar May 15 '21 at 21:12

score 0 · Answer 8 · answered May 15 '21 at 22:22

If your array has other keys along with "somekey" and you like to separate values corresponding to only "somekey" then try the following:

const array = [{"somekey":"Some Value Pushed"},{"somekey":"Second Value"}, {"otherkey":"other Value"}];

const filteredArray = array.filter((obj) => {
  return  "somekey" in obj
}, []);

const valuesArray = filteredArray.map(obj => obj.somekey);

result = [{"somekey":valuesArray}];

console.log(result)

combining duplicate key's values in JavaScript array

8 Answers8