title: Data transformations with RxJava in Kotlin
body: <p>I'm using Kotlin and I have an <code>Observable&lt;List&lt;FlickPhoto&gt;&gt;</code> model. Each <code>FlickrPhoto</code> contains a List, and each <code>Photos</code> model contains a <code>List&lt;Photo&gt;</code>.</p>
  
  <p>I want to transform a <code>List&lt;FlickrPhoto&gt;</code> to a <code>List&lt;PhotoEntity&gt;</code>, which is basically another model with less data, and wrap it into an <code>Observable</code> (in order to finally get an <code>Observable&lt;List&lt;PhotoEntity&gt;&gt;</code>).</p>
  
  <p>How can I do this in the best RxJava way?
  I have created a <code>PhotoEntityMapper</code> class with the following method that I'm sure could be properly used for the purpose:
  <code>override fun transform(photoCollection: List&lt;Photo&gt;): List&lt;PhotoEntity&gt;</code></p>
  
  <p>Thanks in advance!</p>