title: 2 dataframes with different primary keys
body: <p>So I have been trying to find a solution to merge 2 data frames. the primary keys are matching sometimes and sometimes they are on DF1 but not DF2 and DF2 but not DF1. I want all rows and ID's to be displayed and to give a '-' for values that do not appear. For values that do appear in both I want them to be concatenated in the same row as shown in DF3:</p>
  
  <pre><code>    &gt;&gt;&gt;DF1                             &gt;&gt;&gt;DF2          
      ID  Apples  Oranges  Transaction  ID  Milk  Meat Transaction
      1   2       1        Credit       1   2     3    Cash
      3   3       4        Debit        2   7     2    Cash
      5   2       3        Cash         6   2     3    Cash
  
      &gt;&gt;&gt;DF3
      ID  Apples  Oranges Transaction1  Milk  Meat Transaction2
      1   2       1       Credit        2     3    Cash
      2   -       -       -             7     2    Cash
      3   3       4       Debit         -     -    -
      5   2       3       Cash          -     -    -
      6   -       -       -             2     3    Cash
  </code></pre>