title: Extracting specific selected columns to new DataFrame as a copy
body: <p>I have a pandas DataFrame with 4 columns and I want to create a <strong>new</strong> DataFrame that <strong>only</strong> has three of the columns.  This question is similar to: <a href="https://stackoverflow.com/questions/10085806/extracting-specific-columns-from-a-data-frame">Extracting specific columns from a data frame</a> but for pandas not R.  The following code does not work, raises an error, and is certainly not the pandasnic way to do it. </p>
  
  <pre><code>import pandas as pd
  old = pd.DataFrame({'A' : [4,5], 'B' : [10,20], 'C' : [100,50], 'D' : [-30,-50]})
  new = pd.DataFrame(zip(old.A, old.C, old.D)) # raises TypeError: data argument can't be an iterator 
  </code></pre>
  
  <p>What is the pandasnic way to do it?  </p>