title: pandas iterrows() two data frame
body: <p>I'm doing something that I know that I shouldn't be doing. I'm doing a for loop within a for loop (it sounds even more horrible, as I write it down.) Basically, what I want to do, theoretically, using two dataframes is something like this:</p>
  
  <pre><code>for index, row in df_2.iterrows():
      for index_1, row_1 in df_1.iterrows():
          if row['column_1'] == row_1['column_1'] and row['column_2'] == row_1['column_2'] and row['column_3'] == row_1['column_2']:
              row['column_4'] = row_1['column_4']
  </code></pre>
  
  <p>There has got to be a (better) way to do something like this. Please help!</p>