title: How to sort csv by specific column
body: <p>I try to sort a csv contain temperatures by the 4th column.</p>
  
  <pre><code>Sort -n -k4 temperature.csv
  </code></pre>
  
  <p>As a result I get this:</p>
  
  <pre><code>2017-06-24 11:20,23.57,19.0,16.7,0.087,3.615
  2017-06-24 11:25,23.51,19.0,16.7,0.087,3.689
  2017-06-24 12:45,22.03,19.0,17.1,0.096,4.152
  2017-06-24 13:00,21.92,19.0,17.1,0.096,4.229
  2017-06-24 14:00,22.22,19.0,17.4,0.197,4.639
  2017-06-24 14:25,22.21,19.0,17.5,0.197,4.774
  2017-06-24 15:10,22.30,19.0,17.1,0.134,5.472
  2017-06-24 16:00,22.42,19.0,17.3,0.134,5.93
  2017-06-24 17:45,22.07,21.0,17.0,0.144,6.472
  2017-06-24 18:25,21.90,21.0,16.9,0.15,6.814
  2017-06-24 19:40,23.01,21.0,16.9,0.318,8.503
  </code></pre>
  
  <p>As you can see the 4th column isn't sorted correctly. I would expect 17.5 in tbe first line and 16.7 in the last line.</p>
  
  <p>I also tried this:</p>
  
  <pre><code>sort -n -t. -k4,1n temperature.csv
  </code></pre>
  
  <p>The result is exactly the same as the previous example.
  Can anyone give me a hint?</p>