title: How to 'unstack' all lists in columns of dataframe and combine results pairwise?
body: <p>I have a dataframe with 5 columns, each column containing lists of variable lengths. This is what a row in my dataframe looks like: </p>
  
  <pre><code>               A                                         B
  1 [aircrafts, they, agreement, airplane]  [are, built, made, built] 
  </code></pre>
  
  <p>Now I would like to 'unpack' or 'unstack' these lists so that each cell only contains one value (one word). In the unpacking process, the words in cells from one column should be combined pairwise with the corresponding value in the next column. The result would then be:</p>
  
  <pre><code>        A            B
     1  aircrafts      are 
     2  they           built
     3  agreement      made
     4  airplane       built
  </code></pre>
  
  <p>For reference, my full dataframe looks as follows:</p>
  
  <pre><code>   obj                       rel1  \
  0                                 [Boeing]                    [sells]   
  1   [aircrafts, they, agreement, airplane]  [are, built, made, built]   
  2                       [exception, these]                 [are, are]   
  3                        [sales, contract]       [regulated, consist]   
  4                               [contract]               [stipulates]   
  5                            [acquisition]                      [has]   
  6                               [contract]                  [managed]   
  7                               [employee]                      [act]   
  8                    [salesperson, Boeing]          [change, ensures]   
  9                     [airlines, airlines]            [related, have]   
  10                                [Boeing]                     [keep]   
  
                    dep1                    rel2  \
  0          [aircrafts]                    [to]   
  1                   []              [on, with]   
  2                   []           [of, of, for]   
  3                   []  [by, of, with, of, of]   
  4           [elements]            [across, as]   
  5            [details]       [of, as, of, for]   
  6                   []                    [by]   
  7                   []               [as, for]   
  8                   []  [Given, of, over, for]   
  9            [company]               [to, for]   
  10  [track, aircrafts]   [of, between, to, of]   
  
                                                   dep2  
  0                                         [companies]  
  1                                  [demand, customer]  
  2                            [airplanes, scope, case]  
  3   [means, contracts, companies, acquisitions, ai...  
  4                          [acquisitions, conditions]  
  5                [airplane, model, airplane, options]  
  6                                       [salesperson]  
  7                            [salesperson, contracts]  
  8                     [term, contracts, time, client]  
  9                                    [other, example]  
  10        [relationships, companies, airlines, buyer]        
  </code></pre>
  
  <p>How can I perform the 'unpacking' and rearranging operations in python? It would be great if these operations could be performed on the dataframe itself. If this proves to be difficult or impossible, is there a way I could rearrange the data in the lists before combining them into a dataframe? </p>
  
  <p>Thank you very much for any help or advice. </p>