title: Find row closest value to input
body: <p>I am struggling with this problem. I have an pandas array which looks like this</p>
  
  <pre><code>               delta_n    column_1   ...
  0                10      10        ...
  1                20       0
  2                30       0
  </code></pre>
  
  <p>Now i have a number, lets say i search for <code>delta_n=20.5</code> and I want to select the row closest to the number of delta_n.</p>
  
  <p>My output should be:</p>
  
  <pre><code>1                20       0
  </code></pre>
  
  <p>I tried it with <code>df.loc[20.5]</code> but as it is not in the pd dataframe it doesn't work.</p>
  
  <p>Thanks,
  R</p>