Bug in table indexing  #4672

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1. pllim

   added

   table

   Bug

   on Mar 7, 2016
2. sas987 commented on Mar 16, 2016

   

   sas987

   on Mar 16, 2016

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   after compiling the above program i came to know that in astropy library the functions like add_index and loc have not been included into astropy library when installed into python framework,like i was compiling using spyder in anaconda framework,but it was throwing error that
   'Table' object has no attribute 'add_index'
   and so for the loc function
   plzz mentor reply to my above statement
   asap
3. taldcroft

   added

   Package-expert

   on Mar 17, 2016
4. taldcroft commented on Mar 17, 2016

   

   taldcroft

   on Mar 17, 2016

   Member

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   @sas987 - I have just marked this issue as requiring expert knowledge of the Table package. It is not a good place for you to start.
5. rirze commented on Mar 18, 2016

   

   rirze

   on Mar 18, 2016

   Contributor

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   So it seems that when a new Table is made from a slice of an existing one, it does not carry over its primary_key attribute. This is what is causing the error in index.py:

   key = self.table.primary_key here, primary_key is None
   index = self.indices[key]

   If one inserts a line of code at line 718 on table.py under _new_from_slice(...) :

   self._make_table_from_cols(table, newcols)
table.primary_key = self.primary_key<-------this is the inserted line
   return table

   Then the error does not show. However, I'm not sure this is the right way to patch the error, or if the statement ought to be placed elsewhere.
6. taldcroft commented on Mar 18, 2016

   

   taldcroft

   on Mar 18, 2016

   Member

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   Good catch @rirze! There is one other place to put the line, and for clarity I would move your inserted line up near the self.meta settings:

   diff --git a/astropy/table/table.py b/astropy/table/table.py
   index 9eb65a8..117c762 100644
   --- a/astropy/table/table.py
   +++ b/astropy/table/table.py
   @@ -664,6 +664,7 @@ class Table(object):
            table = data  # data is really a Table, rename for clarity
            self.meta.clear()
            self.meta.update(deepcopy(table.meta))
   +        self.primary_key = table.primary_key
            cols = list(table.columns.values())
   
            self._init_from_list(cols, names, dtype, n_cols, copy)
   @@ -703,6 +704,7 @@ class Table(object):
            table = self.__class__(masked=self.masked)
            table.meta.clear()
            table.meta.update(deepcopy(self.meta))
   +        table.primary_key = self.primary_key
            cols = self.columns.values()
   

   Can you go ahead and make these edits and add tests similar to:

   In [2]: t = simple_table()
   
   In [3]: t.add_index('a')
   
   In [4]: t2 = t[:]
   
   In [5]: t3 = t.copy()
   
   In [6]: t4 = Table(t)
   
   In [7]: t2.primary_key
   Out[7]: ('a',)
   
   In [8]: t3.primary_key
   Out[8]: ('a',)
   
   In [9]: t4.primary_key
   Out[9]: ('a',)
   

   (And of course make sure that .loc works as expected in each case.)
7. taldcroft

   added a commit that references this issue on May 16, 2016

   Make Table inherit primary_key attribute from its parent Table. Add t…

   ...

   0cce20c
8. taldcroft

   closed this as completedin #4930on May 16, 2016