title: How to delete all columns in DataFrame except certain ones?
body: <p>Let's say I have a DataFrame that looks like this:</p>
  
  <pre><code>a  b  c  d  e  f  g  
  1  2  3  4  5  6  7
  4  3  7  1  6  9  4
  8  9  0  2  4  2  1
  </code></pre>
  
  <p>How would I go about deleting every column besides <code>a</code> and <code>b</code>?</p>
  
  <p>This would result in:</p>
  
  <pre><code>a  b
  1  2
  4  3
  8  9
  </code></pre>
  
  <p>I would like a way to delete these using a simple line of code that says, delete all columns besides <code>a</code> and <code>b</code>, because let's say hypothetically I have 1000 columns of data.</p>
  
  <p>Thank you.</p>