I have the following structure:

ley objects = {
   key1: [1, 2, 3],
   key2: [3,4,6],
   key3: [5, 6, 7],
}

How can I bine those arrays keeping any duplicates so I will have [1, 2, 3, 3, 4, 6, 6, 6, 7]? I have tried concat but I cannot seem to find a way to do so. I have many more keys so it has to be some loop:

My attempt so far:

let arr = []
for(const [key, value] of Object.entries(objects)){ 
    arr.concat(value);
}

Would there be a possible way to avoid this loop?

I have the following structure:

ley objects = {
   key1: [1, 2, 3],
   key2: [3,4,6],
   key3: [5, 6, 7],
}

How can I bine those arrays keeping any duplicates so I will have [1, 2, 3, 3, 4, 6, 6, 6, 7]? I have tried concat but I cannot seem to find a way to do so. I have many more keys so it has to be some loop:

My attempt so far:

let arr = []
for(const [key, value] of Object.entries(objects)){ 
    arr.concat(value);
}

Would there be a possible way to avoid this loop?

• javascript

• 3 You mentioned you've "tried concat" - can you include that attempt here, so that the munity might be able to point out where your current approach is flawed? – esqew Commented Mar 25, 2021 at 13:09
• @esqew - my bad, added my attempt – ashes999 Commented Mar 25, 2021 at 13:15
• Why does 6 appear 3 times in your output? What happened to 5? – Nick Parsons Commented Mar 25, 2021 at 13:17
• 2 .concat() produces a new array, so you need to assign it: arr = arr.concat(value) – VLAZ Commented Mar 25, 2021 at 13:17
• Related: Javascript Array Concat not working. Why? and JavaScript: How to join / bine two arrays to concatenate into one array? – VLAZ Commented Mar 25, 2021 at 13:21

6 Answers 6

You could flat the values from the array.

let object = { key1: [1, 2, 3], key2: [3, 4, 6], key3: [5, 6, 7] },
    result = Object.values(object).flat();

console.log(result);

You can use ES6 spread syntax.

const obj = {
  key1: [1, 2, 3],
  key2: [3, 4, 6],
};

const result = [...obj.key1, ...obj.key2];
console.log(result);

In this scenario, I'd use Array.prototype.flat() in conjunction with Object.values():

const obj = {
  key1: [1, 2, 3],
  key2: [3, 4, 6],
};

const result = Object.values(obj).flat();
console.log(result);

You can use Array.prototype.concat(),Array.prototype.reduce() and Object.values().

const obj = {
    key1: [1, 2, 3],
    key2: [3, 4, 6],
    key3: [5, 6, 7]
};

const result = Object.values(obj).reduce((acc, item) => acc.concat(item), []);
console.log(result);

I assume you aim not only to merge the arrays but also to sort them as per your output. In this case, you can loop through the keys and push them in one array. After that, you can sort them by value.

const obj = {
   key1: [1, 2, 3],
   key2: [3,4,6]
};

const unsorted = Object.keys(obj).reduce((acc, key) => {
  acc.push(...obj[key]);
  return acc;
}, []);

const sorted = [...unsorted].sort((a, b) => a - b);

console.log(sorted);

This will also work

    let objects = {
   key1: [1, 2, 3],
   key2: [3,4,6],
   key3: [5, 6, 7],
}
        result = Object.values(objects).join();

console.log(result);