title: Python Pandas merge only certain columns
body: <p>Is it possible to only merge some columns? I have a DataFrame df1 with columns x, y, z, and df2 with columns x, a ,b, c, d, e, f, etc.</p>
  
  <p>I want to merge the two DataFrames on x, but I only want to merge columns df2.a, df2.b - not the entire DataFrame. </p>
  
  <p>The result would be a DataFrame with x, y, z, a, b.</p>
  
  <p>I could merge then delete the unwanted columns, but it seems like there is a better method.</p>