CODEWITHSUNDEEP
rxjsobservabletypescript2.0
Sgt Pepper
Sgt Pepper

Reputation: 13

Rxjs/Typescript: Trying to filter a stream on array intersection

Have a stream, wherein the object contains and array of string. I have a filter which is another array of string. The filter should only emit those items where the intersection of the array is not empty.

This is the psuedo code of what I want to do. 

genreFilter: string["poetry", "fiction"]

this.books$ = this.bookInventoryService.getBooks()
    .filter(book => {
        for( let genre of genreFilter) {
            if (book.genres.contains(genre) {
                return true;
            }
        }
    });

Is there a way to do array intersection?

Upvotes: 1

Views: 7065

Answers (1)

paulpdaniels
paulpdaniels

Reputation: 18663

Not really an Rx question, but if you are compiling to ES6 you can create a Set from the filter and then use the Array#some to determine if there are any intersections.

const genreFilter: Set<string> = new Set(["poetry", "fiction"]);

this.books$ = this.bookInventoryService.getBooks()
    .filter(book => book.genres.some(genre => genreFilter.has(genre)));

If Set is not available you can still do it with an Array if the comparison set is small. Or if the set is large you could create an object out of the filter so you get O(1) lookup:

   const genreFilter = ["poetry", "fiction"]
      .reduce((obj, key) => {
        obj[key] = true 
        return obj;
      }, {});

   this.books$ = this.bookInventoryService.getBooks()
        .filter(book => book.genres.some(genre => genreFilter[genre]));

Upvotes: 1

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