title: returning pairs in an array that match a certain condition
body: <p>so I have to do some data processing and I am hitting a roadblock on how to properly write this once. </p>
  
  <p>I have an array of integers  which can range between 0 and 400.</p>
  
  <p>Now most values will be in a certain range(~100)</p>
  
  <p>I want to find all values who are more than twice as big as eachother. So 2*a >= b.
  E.g if you have 90 and 180. I want to find the index of those and all of those so let's say in the same array I have also a 200. Then I also want to return 90 and 200.</p>
  
  <p>any help is appreciated</p>