CODEWITHSUNDEEP
angulartypescriptrxjsngrx-store
pgcd
pgcd

Reputation: 548

Angular/ngrx - Group and aggregate values from state

I am trying to figure out how to get a grouped and aggregated array of values (that I can use with ngFor) starting from a list of objects, and for the life of me I can't make it work. The data (which is a slice of my state) looks something like this:

[{name: "A", value: 1, desc: 'something irrelevant'}, 
 {name: "A", value: 3, desc: 'also other properties'}, 
 {name: "B", value: 2, desc: 'etc.'}, 
 {name: "B", value: 5, desc: 'etc.'}]

And the result I'm trying to get is something like (note that the type is different):

[{name: "A", value: 4}, {name: "B", value: 7}]

So, basically I want to find the distinct "names" and the sum of "value" for all the objects that have that name, with an output that can be used by ngFor | async.

My almost working solution to get the distinct values, at the moment, is:

       this.aggregates:Observable<any[]> = this.store
        .select(state => state.valuesList)
        .map(valuesList => valuesList.sort((a,b) => {return (a.name > b.name) ? 1 : ((b.name > a.name) ? -1 : 0);} }))
        .flatMap(valuesList => valuesList)
        .map(value => value.name)
        .distinct();

I'd be happy to start with this; the problem is that, if I don't add a toArray(), Typescript complains about "Type string is not assignable to type any[]"; if I add toArray() after distinct(), it doesn't complain anymore but a subscribe() yields no result.

What am I doing wrong? Should I move everything to the reducer (but then I don't know if I can change the type of objects returned by different actions in the same reducer)? Any help is very very much appreciated.

UPDATE: I'd be even happier to have a working groupBy() implementation, since it should be exactly its use case.

Upvotes: 2

Views: 3338

Answers (2)

cartant
cartant

Reputation: 58430

You can use groupBy to do what you want, but you have to use the groupBy operator on an observable derived from the list - as groupBy expects an observable of items.

In the following snippet, slice is equivalent to this.store.select(state => state.valuesList)

const slice = Rx.Observable.of([
  { name: "A", value: 1, desc: "something irrelevant" },
  { name: "A", value: 3, desc: "also other properties" },
  { name: "B", value: 2, desc: "etc." },
  { name: "B", value: 5, desc: "etc." }
]);

const grouped = slice.concatMap(list => Rx.Observable
  .from(list)
  .groupBy(item => item.name)
  .mergeMap(group => group
    .reduce((total, item) => total + item.value, 0)
    .map(total => ({ name: group.key, value: total }))
  )
  .toArray()
);

grouped.subscribe(value => console.log(value));
.as-console-wrapper { max-height: 100% !important; top: 0; }
<script src="https://unpkg.com/rxjs@5/bundles/Rx.min.js"></script>

Upvotes: 3

botika
botika

Reputation: 503

Somethings like this:

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/from';
import 'rxjs/add/operator/map';

function main() {
    const t = [
        { name: "C", value: 3, desc: 'also other properties' },
        { name: "A", value: 1, desc: 'something irrelevant' },
        { name: "B", value: 2, desc: 'etc.' },
        { name: "A", value: 3, desc: 'also other properties' },
        { name: "B", value: 5, desc: 'etc.' }
    ];

    const store = Observable.from(Array(100).fill(t));

    const aggregates: Observable<any[]> = store
    .map((valuesList) => valuesList
        .map((x) => ({ name: x.name, value: x.value }))
        .sort((a, b) => a.name.localeCompare(b.name))
        .reduce((pre, cur) => {
            const len = pre.length - 1;

            if (pre[len] && pre[len].name === cur.name) {
                pre[len].value += cur.value;
                return pre;
            }
            pre[len + 1] = cur;
            return pre;
        }, [])
    );

    return aggregates;
}

main().subscribe((x) => {
    console.dir(x, { depth: null });
});

The output is:

[ { name: 'A', value: 4 },
  { name: 'B', value: 7 },
  { name: 'C', value: 3 } ]
[ { name: 'A', value: 4 },
  { name: 'B', value: 7 },
  { name: 'C', value: 3 } ]
[ { name: 'A', value: 4 },....

Upvotes: 1

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