Rx.JS中的映射序列

Question

I would like to map correct sequence using Rx.js. A simplest example will be using keyboard. I attach Rx.js to keyboard events and waiting for three A no matter what will be between them, except Q. When sequence is matched I would like to print OK on console. For example:

• AAA -> should print OK
• AsssAqweA -> should print OK
• AAQAAQ -> shouldn't print anything
• AAQAAA -> should print OK
• AAAsssAAAsssAAA -> should print three times OK

Should I use filter function and keep state inside it? Or there is an esier way to do that.

Answer 1

You should be able to use the filter and scan operators to do what you want:

 Rx.Observable.from("AsssAqweAbAAQAAA") // Only A and Q characters are important: .filter(char => (char === "A") || (char === "Q")) // Accumulate the A characters until there are three // or until a Q is received: .scan((acc, char) => { if ((char === "Q") || (acc.length === 3)) { acc = []; } if (char === "A") { acc.push(char); } return acc; }, []) // Filter the accumulated characters until there // are three: .filter(acc => acc.length === 3) .mapTo("OK") .subscribe(value => console.log(value)); 

 <script src="https://unpkg.com/rxjs@5/bundles/Rx.min.js"></script> 

Answer 2

You could try it with a bufferCount - though I'm not certain if your given examples are simplified and in reality a little more complex, but maybe this helps:

 const source$ = Rx.Observable.from("aaqassaaassaaa"); source$.bufferCount(3, 1) // .do(console.log) // uncomment to see the processed data .filter(data => data.join("") === "aaa") // your detection-logic .mapTo("Ok") .subscribe(console.log); 

 <script src="https://unpkg.com/rxjs/bundles/Rx.min.js"></script>