Javascript - How to get unique values from an array of objects in a Map?

TRao
January 16, 2025
100 views
0 votes
2 Answers

I have a Map in the following format.

const a = [{ data: ['name1', true, true] }, { data: ['name2', false, true] }];
const b = [{ data: ['name3', true, true] }, { data: ['name2', false, true] }];
const c = [];

const map = new Map();
map.set('a', a);
map.set('b', b);
map.set('c', c);

const expectedData = [
  ['name1', true, true],
  ['name2', false, true],
  ['name3', true, true],
]; // remove duplicates and empty arrays. name2 is included only once in the final array

I tried using the spread operator and creating a new set of elements. But the final array includes all the occurrences of ‘name2’ such as: [[‘name1’, true, true], [‘name2’, false, true], [‘name2’, false, true], [‘name3’, true, true]].

Is there an easy way to filter the map’s values based on the first element of the array?

Tags: arrays javascript

Answers

Loop over all the objects in the map. Use a Set to hold the names that have been added to the result, so you only add a name once.

const map = new Map();
map.set('a', a);
map.set('b', b);
map.set('c', c);

const result = [];
const names = new Set();
map.entries().forEach(([key, array]) =>
  array.forEach(({
    data
  }) => {
    if (!names.has(data[0])) {
      names.add(data[0]);
      result.push(data);
    }
  })
);

console.log(result);

<script>
  const a = [{
    data: ['name1', true, true]
  }, {
    data: ['name2', false, true]
  }];
  const b = [{
    data: ['name3', true, true]
  }, {
    data: ['name2', false, true]
  }];
  const c = [];
</script>

- NickParsons
- January 16, 2025 at 12:57 am
- 0 votes
0
One option is to map your array of data into an array of arrays with .flatMap() and .map(), giving you:
```
[['name1', true, true], ['name2', false, true], ['name3', true, true]]
```
and then using Map.groupBy() on this array to create a Map grouped by the first element (name). Once you have this group, you can use Array.from() to get the first unique name entry and convert the map into an array:
const a = [{ data: ['name1', true, true] }, { data: ['name2', false, true] }]; const b = [{ data: ['name3', true, true] }, { data: ['name2', false, true] }]; const c = []; const arrays = [a, b, c]; const grouped = Map.groupBy(arrays.flatMap(arr => arr.map(o => o.data)), ([name]) => name); const res = Array.from(grouped, ([,[first]]) => first); console.log(res);
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