Pandas unstack problems ValueError Index contains duplicate entries cannot reshape

Question

I am trying to unstack a multi-index with pandas and I am keep getting   ValueError  Index contains duplicate entries  cannot reshape   Given a dataset with four columns    id  string  date  string  location  string  value  float    I first set a three-level multi-index   In  37   e set index   id    date    location    inplace True   In  38   e Out 38                                        value id           date       location        id1          2014-12-12 loc1        16 86              2014-12-11 loc1        17 18              2014-12-10 loc1        17 03              2014-12-09 loc1        17 28   Then I try to unstack the location   In  39   e unstack  location   --------------------------------------------------------------------------- ValueError                                Traceback  most recent call last   lt ipython-input-39-bc1e237a0ed7 gt  in  lt module gt    ---- gt  1 e unstack  location       C  Anaconda envs sandbox lib site-packages pandas core reshape pyc in  make selectors self      143      144         if mask sum    lt  len self index   -- gt  145             raise ValueError  Index contains duplicate entries        146                               cannot reshape       147   ValueError  Index contains duplicate entries  cannot reshape   What is going on here

User · Answer

There s a far more simpler solution to tackle this   The reason why you get ValueError  Index contains duplicate entries  cannot reshape is because  once you unstack  Location   then the remaining index columns  id  and  date  combinations are no longer unique    You can avoid this by retaining the default index column  row    and while setting the index using  id    date  and  location   add it in  append  mode instead of the default overwrite mode    So use    e set index   id    date    location    append True    Once this is done  your index columns will still have the default index along with the set indexes  And unstack will work   Let me know how it works out

User · Answer

Here s an example DataFrame which show this  it has duplicate values with the same index  The question is  do you want to aggregate these or keep them as multiple rows   In  11   df Out 11      0  1  2      3 0  1  2  a  16 86 1  1  2  a  17 18 2  1  4  a  17 03 3  2  5  b  17 28  In  12   df pivot table values 3  index  0  1   columns 2  aggfunc  mean      desired  Out 12   2        a      b 0 1 1 2  17 02    NaN   4  17 03    NaN 2 5    NaN  17 28  In  13   df1   df set index  0  1  2    In  14   df1 Out 14              3 0 1 2 1 2 a  16 86     a  17 18   4 a  17 03 2 5 b  17 28  In  15   df1 unstack 2  ValueError  Index contains duplicate entries  cannot reshape     One solution is to reset index  and get back to df  and use pivot table   In  16   df1 reset index   pivot table values 3  index  0  1   columns 2  aggfunc  mean   Out 16   2        a      b 0 1 1 2  17 02    NaN   4  17 03    NaN 2 5    NaN  17 28   Another option  if you don t want to aggregate  is to append a dummy level  unstack it  then drop the dummy level

User · Answer

I had such problem  In my case problem was in data - my column  information  contained 1 unique value and it caused error  UPDATE  to correct work  pivot  pairs  id user information  cannot have duplicates  It works   df2   pd DataFrame   id user   1 2 3 4 4 5 5     information    phon   phon   phone   phone1   phone   phone1   phone      value    1   01 01 00    01 02 00   2   01 03 00   3   01 04 00     df2 pivot index  id user   columns  information   values  value     it doesn t work   df2   pd DataFrame   id user   1 2 3 4 4 5 5     information    phone   phone   phone   phone   phone   phone   phone      value    1   01 01 00    01 02 00   2   01 03 00   3   01 04 00     df2 pivot index  id user   columns  information   values  value     source  https   stackoverflow com a 37021196 6088984

[python] Pandas unstack problems: ValueError: Index contains duplicate entries, cannot reshape

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