How can I concatenate objects inside an array with matching IDs? [duplicate]

Question

I'm receiving an array of objects saying which events have changed. The following code is an example of such change. There are other fields that could change as well, but they won't appear here.

[{ "eventId": "1", "name": "name_a", "isCancelled": "true"},
{ "eventId": "1", "name": "name_a", "date": "2018-11-17T00:00:00.000Z"},
{ "eventId": "2", "name": "name_b", "Status": "Postponed"},
{ "eventId": "3", "name": "name_c", "isCancelled": "true"},
{ "eventId": "3", "name": "name_c", "status": "Private"}]

Is there a way that I can combine the objects with the same ID? Something similar to this.

[{ "eventId": "1", "name": "name_a", "isCancelled": "true", "date": "2018-11-17T00:00:00.000Z"},
{ "eventId": "2", "name": "name_b", "Status": "Postponed"},
{ "eventId": "3", "name": "name_c", "isCancelled": "true", "status": "Private"}

I've seen a lot of threads and they're mostly focused on combining 2 arrays by matching their IDs.

@MaorRefaeli I did try many ways. I didn't post any since most of them didn't work. — Yoel Lorenzo
– Yoel Lorenzo, Commented Nov 20, 2018 at 12:25

Nitish Narang · Accepted Answer · 2018-11-20 12:56:59Z

3

You can use for .. of like below to loop through every element and then based on event id concat the objects

let arr = [{ "eventId": "1", "name": "name_a", "isCancelled": "true"},
{ "eventId": "1", "name": "name_a", "date": "2018-11-17T00:00:00.000Z"},
{ "eventId": "2", "name": "name_b", "Status": "Postponed"},
{ "eventId": "3", "name": "name_c", "isCancelled": "true"},
{ "eventId": "3", "name": "name_c", "status": "Private"}]

let o = {}
for(let d of arr) {
  o[d['eventId']] = { ...(o[d['eventId']] || {}), ...d }
}

console.log(Object.values(o))

edited Nov 20, 2018 at 12:56

answered Nov 20, 2018 at 12:14

Nitish Narang

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5 Comments

Yoel Lorenzo Over a year ago

Thank you very much! I really hate just copying and pasting it. Any recommendations on what topics of JS to study to get better at problem solving?

HMR Over a year ago

Using reduce with Map would probably cleaner.

[   ...arr     .reduce(       (result, item) =>         result.set(item.eventId, {           ...(result.get(item.eventId) || {}),           ...item,         }),       new Map(),     )     .values(), ]

Nitish Narang Over a year ago

@HMR It's matter of choice I believe. I pick reduce and for...of interchangeably. Given this problem, I found for..of to be cleaner (again personal choice). Reg: use of new Map() I personally favour using map where we would need to get rid of duplicates.. Having said that it's again personal decision and we are all correct at the same time. End of the day code must be clean, fast, and readible. Thank you for mentioning though. :)

Nitish Narang Over a year ago

@YoelLorenzo Hmm.. Firstly, get yourself comfortable with "Array.map", reduce, filter, find, for.. of and solve as many problems as you can. Best way I found is - search questions on stackoverflow - solve yourself and then look for others answers and see how you could have done differently. With time you will get better. :)

Yoel Lorenzo Over a year ago

@NitishNarang Thank you very much! I'll try my best.

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