Cancat object values as a sting based on another object value

Question

I have a js array as follows.

[{"id":"1","name":"John","city":"London"},
{"id":"2","name":"Paul","city":"Darvin"},
{"id":"1","name":"Ron","city":"Paris"},
{"id":"2","name":"Will","city":"Tokyo"},
{"id":"3","name":"Dave","city":"Oslo"}]

I want to concat values in "name" and "city" based on "id" values. The final result should look like this.

[{"id":"1","name":"John,Ron","city":"London,Paris"},
 {"id":"2","name":"Paul,Will","city":"Darvin,Tokyo"},
 {"id":"3","name":"Dave","city":"Oslo"}]

Answer 1

Group array of objects by key.

var arr = [{"id":"1","name":"John","city":"London"},
{"id":"2","name":"Paul","city":"Darvin"},
{"id":"1","name":"Ron","city":"Paris"},
{"id":"2","name":"Will","city":"Tokyo"},
{"id":"3","name":"Dave","city":"Oslo"}]

var result = Object.values(arr.reduce(function(agg, item) {
  agg[item.id] ??= {id: item.id, name: [], city: []}
  agg[item.id].name.push(item.name)
  agg[item.id].city.push(item.city)
  return agg
}, {})).map(function(item) {
  item.city = item.city.join(",");
  item.name = item.name.join(",");
  return item;
})

console.log(result);