title: PANDAS: Trim multiple data frames
body: <p>I want to remove rows from several data frames so that they are all length n.  When I tried to use a -for- loop, the changes would not persist through the rest of the script. </p>
  
  <pre><code>n = 50
  groups = [df1, df2, df3]
  for dataset in groups:
      dataset = dataset[:n]
  </code></pre>
  
  <p>Redefining names individually (e.g., df1 = df1[:n] ), works, but what are some alternate ways?  (Either through python or pandas) </p>
  
  <p>More importantly, why does the -for- loop not work here?</p>
  
  <p>pandas == 0.10.1 
  python == 2.7.3</p>