A Saturday 05 December 2009 02:06:47 Jon Olav Vik escrigué: > I have many sorted tables of identical structure and would like to combine > them into a single, sorted table. Python >= 2.6 offers > heapq.merge(*iterators), but I cannot quite get it to work. Could somebody > please tell me how to convert a list of Table instances into a list of > iterators that heapq.merge() can use? > > I'm particularly puzzled by the following (can be run after the code > below). Note that t[0] is a Table object. > > In [74]: for row in t[0]: print row > ....: > (0, 100.0) > (3, 103.0) > (6, 106.0) > (9, 109.0) > > In [75]: [row for row in t[0]] > Out[75]: [(9, 109.0), (9, 109.0), (9, 109.0), (9, 109.0)]
Yup, this is a FAQ. The `row` object is in fact an *accessor* to data, not a data container by itself. This is the reason why: for row in t[0]: print row works well, because the accessor is *used* on every iteration. However, in: [row for row in t[0]] you are only appending the *same* instance of the accessor each time. Instead, you may want to use: [row[:] for row in t[0]] or, if you want NumPy objects instead of tuples: [row.fetch_all_fields() for row in t[0]] See http://www.pytables.org/docs/manual/ch04.html#RowClassDescr for more info. HTH, -- Francesc Alted ------------------------------------------------------------------------------ Join us December 9, 2009 for the Red Hat Virtual Experience, a free event focused on virtualization and cloud computing. Attend in-depth sessions from your desk. Your couch. Anywhere. http://p.sf.net/sfu/redhat-sfdev2dev _______________________________________________ Pytables-users mailing list Pytables-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/pytables-users
