title: How to split a string into substrings of a given length?
body: <p>I have a string such as:</p>
  
  <p><code>"aabbccccdd"</code></p>
  
  <p>I want to break this string into a vector of substrings of length 2 :</p>
  
  <p><code>"aa" "bb" "cc" "cc" "dd"</code></p>