JS merge Array of the Maps to a single Map

Question

I have a structure of

Array(4) [Map(1),Map(1),Map(1),Map(1)]

All keys are different there. I am trying find the common way to merge it in one Map.

I know the way for two Maps:

let merged = new Map([...first, ...second])

But for this solution I need more common way.

reduce might be a way?

cmgchess
– cmgchess

2022-07-16 19:15:05 +00:00
Commented Jul 16, 2022 at 19:15 — cmgchess
– cmgchess, Commented Jul 16, 2022 at 19:15
@cmgchess it seems flatMap is a more short way, thanks

Uladzislau Kaminski
– Uladzislau Kaminski

2022-07-16 19:23:57 +00:00
Commented Jul 16, 2022 at 19:23 — Uladzislau Kaminski
– Uladzislau Kaminski, Commented Jul 16, 2022 at 19:23

ulou · Accepted Answer · 2022-07-16 19:20:41Z

6

You are looking for flatMap:

const arr = [
  new Map([[1, 2]]),
  new Map([[3, 4]]),
];

const merged = arr.flatMap(e => [...e])

console.log(merged)

answered Jul 16, 2022 at 19:20

ulou

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CertainPerformance · Accepted Answer · 2022-07-16 19:16:11Z

1

.map each map to its entries, then flatten the array of arrays of entries to just a single array of entries, then turn that into a Map.

const arr = [
  new Map([[1, 2]]),
  new Map([[3, 4]]),
];

const merged = new Map(
  arr.map(
    map => [...map]
  ).flat()
);
console.log([...merged]);

answered Jul 16, 2022 at 19:16

CertainPerformance

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Comments

Mina · Accepted Answer · 2022-07-16 19:20:00Z

0

You can use array#reduce to merge multiple Map.

maps.reduce((r, map) => new Map([...r, ...map]), new Map())

const map1 = new Map();
map1.set('a', 1);
const map2 = new Map();
map2.set('b', 2);
const map3 = new Map();
map3.set('c', 3);

const maps = [map1, map2, map3],
      merged = maps.reduce((r, map) => new Map([...r, ...map]), new Map());
console.log([...merged]);

edited Jul 16, 2022 at 19:20

Mina

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answered Jul 16, 2022 at 19:18

Hassan Imam

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