How can I merge the columns of two data frames, containing a distinct set of columns but some rows with the same names? The fields for rows that don't occur in both data frames should be filled with zeros:

> d
    a   b   c   d   e   f   g   h   i  j
1 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10
2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  1
> e
   k  l  m  n  o  p  q  r  s  t
1 11 12 13 14 15 16 17 18 19 20
3 21 22 23 24 25 26 27 28 29 30
> de
    a   b   c   d   e   f   g   h   i  j  k  l  m  n  o  p  q  r  s  t
1 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 11 12 13 14 15 16 17 18 19 20
2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  1  0  0  0  0  0  0  0  0  0  0
3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  0 21 22 23 24 25 26 27 28 29 30
r merge dataframe
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