title: Equivalent of Swift's .map in Objective C?
body: <p>Say I have <code>NSArray *x = @[@1, @2, @3, @4];</code></p>
  
  <p>Now say I want an array like <code>@[@2, @4, @6, @8]</code></p>
  
  <p>In good ole Swift, I can just do :</p>
  
  <pre><code>xDoubled = x.map({($0) * 2})
  </code></pre>
  
  <p>Can someone tell me how I can do this in Objective-C without doing -</p>
  
  <pre><code>NSMutableArray *xDoubled = [NSMutableArray new];
  for (NSInteger xVal in x) {
      [xDoubled addObject:xVal * 2];
  }
  </code></pre>
  
  <p>?</p>