javascript - Grouping object entries into object arrays

Question

How can I create arrays to group members depending on their tag?

Tags can be anything, these are just examples.

Example Input

[
  { tag: 'Red', member: 'Red-Steve' },
  { tag: 'Red', member: 'Red-Adam' },
  { tag: 'Blue', member: 'Blue-John' },
  { tag: 'Blue', member: 'Blue-James' },
  { tag: 'Blue', member: 'Blue-Igor' }
]

Example Output

{
  Red: ['Red-Steve', 'Red-Adam']
  Blue: ['Blue-John', 'Blue-James', 'Blue-Igor']
}

---

Edit: I just made a test case on jsperf to compare the efficiency of the different answers and also the answer from the suggested duplicate question https://jsperf.com/group-objects-reduce-vs-for-loop

The answer by @Majed Badawi was the most efficient

标签： javascriptarraystypescriptjavascript-objects

Answer 1

You can use a simple set to group them by tag as follows:

let list = [
            { tag: 'Red', member: 'Red-Steve' },
            { tag: 'Red', member: 'Red-Adam' },
            { tag: 'Blue', member: 'Blue-John' },
            { tag: 'Blue', member: 'Blue-James' },
            { tag: 'Blue', member: 'Blue-Igor' }
];
let set = {};
for(let i = 0; i < list.length; i++){
     let current = list[i];
     if(!set[current.tag])
          set[current.tag] = [current.member];
     else
          set[current.tag].push(current.member);
}
console.log(set);