Flattening nested Observables.subscribe
<p>I am new to <code>Observables</code> with rx.js and I wanted to know how I can flatten the following callback hell:</p>

<pre><code>function getdata1 (argument) {
    return this.http.get(url)
        .map((res: Response) =&gt; res.json());
}

function getdata2 (argument) {
    return this.http.get(url)
        .map((res: Response) =&gt; res.json());
}

getdata1.subscribe((data1: any) =&gt; {
    console.log("got data one. get data 2 now");
    getdata2.subscribe((data2: any) =&gt; {
        console.log("got data one and two here");
    });
});
</code></pre>

<p>I know if this was Promises, <code>then()</code> could have been used to flatten it. But I do not know the equivalent of <code>then()</code> in <code>Observables</code>.</p>