RxJS groupBy to multidimensional array - rxjs

Question

I've been attempting multiple combinations of operators and can't quite get the output I want. Give an array of events:
const events = [
{ day: 1, title: 'Event 1' },
{ day: 1, title: 'Event 2' },
{ day: 1, title: 'Event 3' },
{ day: 2, title: 'Event 4' },
{ day: 2, title: 'Event 5' },
{ day: 2, title: 'Event 6' },
{ day: 'both', title: 'Sandbox 1' },
{ day: 'both', title: 'Sandbox 2' },
]
I'd like an output like so:
[
[
{
"day": 1,
"title": "Event 1"
},
{
"day": 1,
"title": "Event 2"
},
{
"day": 1,
"title": "Event 3"
}
],
[
{
"day": 2,
"title": "Event 4"
},
{
"day": 2,
"title": "Event 5"
},
{
"day": 2,
"title": "Event 6"
}
],
[
{
"day": "both",
"title": "Shared 1"
},
{
"day": "both",
"title": "Shared 2"
}
]
]
The only way I've been able to get this is by subscribing and pushing the result into another array. Ideally the rx chain would build it before subscribing, but I can't quite get it.
Here's what I have that outputs the result above:
from(events).pipe(
groupBy(obj => obj.day),
mergeMap(group => group.pipe(toArray())),
).subscribe(next => {
this.all.push(next)
console.log(this.all)
})

Answer 1

To accumulate the groups into an outer array, you can use another toArray operator after the mergeMap:
from(events).pipe(
groupBy(obj => obj.day),
mergeMap(group => group.pipe(toArray())),
toArray(),
).subscribe(results => console.log(results))
The resultant observable will emit only once and will emit a single array containing all of the group arrays.