Group By Statuses using reduce

Question

I have been using reduce() method to group by Open and Closes statuses (Status_111, Status_222, etc) which then creates an array of which Ids (item.Id) it is associated with.

Code is working and with an expected result, however, I feel like code could have been written better because as you can see I have been using too many if conditions for creating blank arrays to check if (item.Open && !obj[item.Open]) and if (item.Close && !obj[item.Close]) exists - how would you improve the code?

const items = [
 { Id: 100, Open: 'Status_111', Close: 'Status_111' },
 { Id: 200, Open: 'Status_111', Close: 'Status_222' },
 { Id: 300, Open: 'Status_333', Close: 'Status_444' }
]
function groupByOpenAndClose(items) {
 return items.reduce(function (obj, item) {
 if (item.Open && !obj[item.Open]) {
 obj[item.Open] = {
 Open: [],
 Close: []
 }
 }
 if (item.Close && !obj[item.Close]) {
 obj[item.Close] = {
 Open: [],
 Close: []
 }
 }
 if (obj[item.Open]) {
 obj[item.Open].Open.push(item.Id)
 }
 if (obj[item.Close]) {
 obj[item.Close].Close.push(item.Id)
 }
 return obj
 }, {});
}
console.log(groupByOpenAndClose(items));

Answer 1

Like this:

function groupByOpenAndClose(items) {
 return items.reduce((obj, item) => {
 return {
 ...obj,
 [item.Close]: {
 Close: [...(obj[item.Close]?.Close ?? []), item.Id],
 Open: obj[item.Close]?.Open ?? []
 },
 [item.Open]: {
 Open: [...(obj[item.Open]?.Open ?? []), item.Id],
 Close: obj[item.Open]?.Close ?? []
 }
 }
 }, {});
}

But in all seriousness, it is not much you can do without creating some structure of your own - something like default dict in python:

class DefaultDict {
 constructor(defFactory) {
 this.defFactory = defFactory;
 this.dict = {}
 }
 
 getOrDefault(status) {
 if(!status) return;
 if(!this.dict[status]) this.dict[status] = this.defFactory();
 
 return this.dict[status];
 }
}
function groupByOpenAndClose(items) {
 return items.reduce(function(obj, item) {
 obj.getOrDefault(item.Close)?.Close.push(item.Id);
 obj.getOrDefault(item.Open)?.Open.push(item.Id);
 return obj;
 }, new DefaultDict(() => ({ Close: [], Open: [] })));
}
console.log(groupByOpenAndClose(items).dict);