A Tuesday 15 January 2008, Luca Della Santina escrigué: > I'd like to add basic spreadsheet-like functionalities to my > application which bases its data model upon pytables, I was looking > for a way to modify the structure of an exsistent Table, in > particular: > > 1) How to move/insert a column into the Table > 2) How to change the type of a column and convert its data > 3) How to change the name of a column > > If I well understood, by design the structure of columns defined for > a table (by the custom tables.IsDescription subclass) is not meant to > be directly changed by the user after the table is created. > > Users may circumnavigate the problem creating a temporary table with > the desidered column structure and then merge the old column values > into the new table structure, like it is shown in the example > "add-column.py" of pytables' documentation, but obviously it is not > an efficient approach compared to an in-place change of column > properties. > > Are there are alternative ways to accomplish these task? If not, is > there space in pytables development plans to enhance the > possibilities to modify the columns' structure of a table?
Plainly said, there is right now no alternatives for altering the structure of a table without rewriting it entirely. This is why PyTables has to be mostly useful for (very fast access to) read-only data and (fast) row appends or updates. Doing 1) and 2) in a effective way is not impossible, but would require an implementation of column-wise tables first (columns in PyTables are row-wise right now). Of course, this is a recurrent issue that has been discussed several times on this list, but as the implementation is, to say the least, not easy, that should wait until we have time and resources enough (or someone steps ahead and contributes one!). Doing 3) should not require column-wise tables at all, but it is not implemented yet (and should be not very difficult; volunteers?). Ciao, -- >0,0< Francesc Altet http://www.carabos.com/ V V Cárabos Coop. V. Enjoy Data "-" ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Pytables-users mailing list Pytables-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/pytables-users
