title: Join on first column of two files
body: <p>How can I join two files by the first column of each?</p>
  
  <p>file1:  </p>
  
  <pre><code>116
  116
  116
  116
  116
  117
  117
  117
  117
  117
  </code></pre>
  
  <p>file2:</p>
  
  <pre><code>1   37.8378378378378
  2   30.5009605438156
  3   35.4106079490375
  4   25.6565656565657
  .....
  .....
  116 49.4073275862069
  117 25.8182578688696
  118 36.1389759665622
  119 36.7218282111899
  120 55.1587301587302
  </code></pre>
  
  <p>I want to match the 1st columns in both files and print like this:</p>
  
  <pre><code>116  49.4073275862069
  116  49.4073275862069  
  116  49.4073275862069 
  116  49.4073275862069 
  116  49.4073275862069 
  117  25.8182578688696
  117  25.8182578688696
  117  25.8182578688696
  117  25.8182578688696
  117  25.8182578688696
  </code></pre>