Exploring the utilization of grouping keys within the GroupBy operator in RxJS

Question

Exploring the utilization of grouping keys within the GroupBy operator in RxJS

After receiving a structured response from an API,

I come across the following signature:

methodApi(): Observable(Array<MyClass>)

The data looks like this:

{ id: 1, name: 'Red', parentId: null }
{ id: 2, name: 'Apple', parentId: 1 }
others

My goal is to group this data by parentId.

methodApi()
.pipe(groupby((x: MyClass[] => ...))) // THIS IS WHERE THE ISSUE LIES
.subscribe(x => console.log(x));

The methodApi returns Observable<Array>. The problem arises when I attempt to reference the parentId property within the 'groupby' method since it requires an array as input and not a specific object like MyClass.

How can I effectively resolve this grouping issue?

Running Angular 9.0 with RxJS 6.5.5

angular typescript rxjs grouping angular9

Answer 1

Answer №1

To transform your array into an observable stream, you can utilize the from method to create a new stream. Then, by using groupBy, you can group the items based on a specific criteria before converting it back into an array:

methodApi().pipe(
  concatMap((result) => from(result)),
  groupBy((item) => item.parentId),
  mergeMap(group => group.pipe(toArray()))
).subscribe(x => console.log(x));

Check out this example

Alternatively, you can also achieve the same result using mergeAll:

methodApi().pipe(
  mergeAll(),
  groupBy((item) => item.parentId),
  mergeMap(group => group.pipe(toArray()))
).subscribe(x => console.log(x));

See this example for reference

Answer 2

To transform your array into an observable stream, you can utilize the from method to create a new stream. Then, by using groupBy, you can group the items based on a specific criteria before converting it back into an array:

methodApi().pipe(
  concatMap((result) => from(result)),
  groupBy((item) => item.parentId),
  mergeMap(group => group.pipe(toArray()))
).subscribe(x => console.log(x));

Check out this example

Alternatively, you can also achieve the same result using mergeAll:

methodApi().pipe(
  mergeAll(),
  groupBy((item) => item.parentId),
  mergeMap(group => group.pipe(toArray()))
).subscribe(x => console.log(x));

See this example for reference

Answer 3

Answer №2

To achieve this, you can utilize the groupBy operator in the following manner:

methodApi().pipe(
  groupBy((item) => item.parentId),
  mergeMap(group => group.pipe(toArray()))
).subscribe(console.log) // This code snippet will provide you with an array grouped by parentId

Answer 4

To achieve this, you can utilize the groupBy operator in the following manner:

methodApi().pipe(
  groupBy((item) => item.parentId),
  mergeMap(group => group.pipe(toArray()))
).subscribe(console.log) // This code snippet will provide you with an array grouped by parentId

Answer 5

Answer №3

The functionality of the RxJs group by operator is being misunderstood in this context. Instead of grouping objects emitted by the stream, the goal here is to group items within an array that is also emitted by the stream. To achieve this, a custom group by function tailored for arrays, rather than observables, is required. A simple solution would involve using a reduce method to organize the items into an object structure with the parentId serving as the key.

methodApi()
.pipe(map(results => results.reduce(
  (group, item) => {
    if (group[item.parentId]) {
      group[item.parentId].push(item);
    } else {
      group[item.parentId] = [item];
    }
    return group;
  }, {})
)).subscribe(group => {});

Answer 6

The functionality of the RxJs group by operator is being misunderstood in this context. Instead of grouping objects emitted by the stream, the goal here is to group items within an array that is also emitted by the stream. To achieve this, a custom group by function tailored for arrays, rather than observables, is required. A simple solution would involve using a reduce method to organize the items into an object structure with the parentId serving as the key.

methodApi()
.pipe(map(results => results.reduce(
  (group, item) => {
    if (group[item.parentId]) {
      group[item.parentId].push(item);
    } else {
      group[item.parentId] = [item];
    }
    return group;
  }, {})
)).subscribe(group => {});

Exploring the utilization of grouping keys within the GroupBy operator in RxJS

Answer №1

Answer №2

Answer №3

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