title: Joining 4 dataframes that have the same column
body: <p>How do I join together 4 DataFrames? The names of the DataFrames are called df1, df2, df3, and df4.
  They are all the same column size and I am trying to use the 'inner' join.</p>
  <p>How would I modify this code to make it work for all four?</p>
  <p>I tried using this code and it worked to combine two of them, but I could not figure out how to write it to work for all four DataFrames.</p>
  <pre><code>dfJoin = df1.join(df2,how='inner')
  
  print(dfJoin)
  </code></pre>