converting several comma-separated lists into a table, one column per list

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand{\magicFunction}{m}
 {
  \jason_magic:n { #1 }
 }

\int_new:N \l__jason_magic_cols_int
\int_new:N \l__jason_magic_rows_int
\tl_new:N \l__jason_magic_table_tl

\cs_new_protected:Nn \jason_magic:n
 {
  \int_zero:N \l__jason_magic_cols_int
  \int_zero:N \l__jason_magic_rows_int
  \tl_map_inline:nn { #1 }
   {
    \int_incr:N \l__jason_magic_cols_int
    \__jason_magic_makeclist:n { ##1 }
   }
  \__jason_magic_maketable:
  % print the table
  \begin{tabular}{ c *{\l__jason_magic_cols_int}{c} }
  \l__jason_magic_table_tl
  \end{tabular}
 }

% syntactic sugar for avoiding long strings
\cs_new:Nn \__jason_magic_clist:n
 {
  l__jason_magic_ \int_eval:n { #1 } _clist
 }

% store the parts in clists and get the number of rows
\cs_new_protected:Nn \__jason_magic_makeclist:n
 {
  \clist_clear_new:c { \__jason_magic_clist:n { \l__jason_magic_cols_int } }
  \clist_set:cn { \__jason_magic_clist:n { \l__jason_magic_cols_int } } { #1 }
  \int_set:Nn \l__jason_magic_rows_int
   {
    \int_max:nn
     { \l__jason_magic_rows_int }
     { \clist_count:c { \__jason_magic_clist:n { \l__jason_magic_cols_int } } }
   }
 }

\cs_new_protected:Nn \__jason_magic_maketable:
 {
  % make the first row
  \tl_set:Nn \l__jason_magic_table_tl { Problem~number }
  \int_step_inline:nn { \l__jason_magic_cols_int }
   {
    \tl_put_right:Nx \l__jason_magic_table_tl
     {
      & Form~\int_to_Alph:n { ##1 }
     }
   }
  \tl_put_right:Nn \l__jason_magic_table_tl { \\ \hline }
  % make the following rows
  \int_step_inline:nn { \l__jason_magic_rows_int }
   {
    \tl_put_right:Nx \l__jason_magic_table_tl { ##1 }
    \int_step_inline:nn { \l__jason_magic_cols_int }
     {
      \tl_put_right:Nx \l__jason_magic_table_tl
       {
        & \clist_item:cn { \__jason_magic_clist:n { ####1 } } { ##1 }
       }
     }
    \tl_put_right:Nn \l__jason_magic_table_tl { \\ }
    \int_if_odd:nF { ##1 } { \tl_put_right:Nn \l__jason_magic_table_tl { \hline } }
   }
 }

\ExplSyntaxOff

\begin{document}

\magicFunction{ 
    {b, b, a, a, b, b, c}% Test Form A, form is first entry.
    {a, b, c, c, e, a, a}% Test form B
    {c, c, c, a, a, b, c}% Test form C
}

\end{document}

The idea is to allocate a clist for every column. Then the table is built by extracting the relevant item from each clist, by stepping the row index.