title: Combining starts_with with group_by in dplyr
body: <p>I guess it might be a simple trick, but I do not know how to achieve it...</p>
  
  <p>My dateset looks like:</p>
  
  <pre><code>Name, Score
  A a,  20
  A,    30
  B b,   40
  </code></pre>
  
  <p>The output I expect is:</p>
  
  <pre><code>Name, Score
  A,    50
  B,    40
  </code></pre>
  
  <p>In one word, sum the scores that have names which start with the same word (before the space if there is one). I hope the example is self-explanatory. :)</p>
  
  <p>PS: The faster the code runs, the better. The dataset is huge...</p>