Calculating the number of entities in an array using RxJS observable in Typescript (Angular 4)

Question

Calculating the number of entities in an array using RxJS observable in Typescript (Angular 4)

I'm struggling to figure out how to retrieve the number of elements in an array-like Observable without getting back another Observable. I've spent a lot of time experimenting with different operators, but none have been successful.

Here's my current code snippet:

entities: Observable<entity>;

let data = await this.myService.filter(2)
                    .subscribe(d => {this.entities= d; })

I am using Angular HttpClient, which directly sends an Observable from the response. The service code is quite straightforward:

filter(arg: int): Observable<any> {
    return this.http.get<entity>('/api/ent/find/' + arg.toString());}

The entities Observable is typically loaded with multiple entities that I use in a grid. All I need is something like

howMany: number = entities.count() or entities.length()..

.

To get the quantity for use in the component (not display). However, every approach I've tried has resulted in returning an Observable instead of a simple number.

angular typescript rxjs observable

Answer 1

Answer №1

If my interpretation is correct, you have a situation with an Observable<entity> that may yield an unknown quantity of outcomes and you're interested in determining that quantity. Here's one possible approach:

const entities$: Observable<entity> = this.myService.filter(2).share(); // 1
let results: [entity] = []; // 2
let total: number = 0; // 3

entities$.subscribe(entity => this.results.push(entity)); // 4
entities$.reduce((state, curr) => state + 1, 0).subscribe(num => total = num); // 5

This line sends the request to your service and shares the resulting observable amongst all subscribers. (Without using share, each subscriber will generate its own request).
This variable is utilized for storing the fetched entities.
This variable will keep track of how many entities are delivered by the observable.
This part subscribes to the outcomes from the request and adds the received entities into the results array.
Here, the reduction operation initiates with the value 0 (as set in the last argument). For every new value (curr), it increments the stored value by one and updates it. When entities$ completes, it emits the final count, representing the number of returned entities.

Answer 2

If my interpretation is correct, you have a situation with an Observable<entity> that may yield an unknown quantity of outcomes and you're interested in determining that quantity. Here's one possible approach:

const entities$: Observable<entity> = this.myService.filter(2).share(); // 1
let results: [entity] = []; // 2
let total: number = 0; // 3

entities$.subscribe(entity => this.results.push(entity)); // 4
entities$.reduce((state, curr) => state + 1, 0).subscribe(num => total = num); // 5

This line sends the request to your service and shares the resulting observable amongst all subscribers. (Without using share, each subscriber will generate its own request).
This variable is utilized for storing the fetched entities.
This variable will keep track of how many entities are delivered by the observable.
This part subscribes to the outcomes from the request and adds the received entities into the results array.
Here, the reduction operation initiates with the value 0 (as set in the last argument). For every new value (curr), it increments the stored value by one and updates it. When entities$ completes, it emits the final count, representing the number of returned entities.

Answer 3

Answer №2

To access the length of the array, you must first subscribe to the Observable.

data$: Observable<Data[]>;
data: Data[];
this.myService.filter(2)
                .subscribe(result => this.data = result);

After that, you can use data.length()

Answer 4

To access the length of the array, you must first subscribe to the Observable.

data$: Observable<Data[]>;
data: Data[];
this.myService.filter(2)
                .subscribe(result => this.data = result);

After that, you can use data.length()

Calculating the number of entities in an array using RxJS observable in Typescript (Angular 4)

Answer №1

Answer №2

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Calculating the number of entities in an array using RxJS observable in Typescript (Angular 4)

Answer №1

Answer №2

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