Re: [Pytables-users] Slicing with index arrays

[Francesc A. <fa...@ca...>]

Hi Peter,

El dl 18 de 07 del 2005 a les 03:06 -0400, en/na travlr va escriure:
> Having recieved the 1.1 release notification, I also noticed the
> "support for indexes" in the 1.0 release. Does this happen to include
> slicing with an index array (a la numarray)? An example would be the
> non-sequential return of: index = numarray.where(...)[0], then applied
> to further pytable retrieval. Also, I didn't notice any mentionings of
> the index improvements in the documentation.

Let me explain some points first. Unfortunately, the "indexing" verb
receives many meanings in computer sciences. When I first announced the
PyTables support for indexing, I meant that it can sort the columns of
tables in order to do faster searches (i.e. values that fulfill some
condition). 

This kind of indexation was actually implemented back in 0.9, although
it was improved in 1.0 to allow the indexation of tables with more than
2**31 columns. In fact, from 1.0 on, all the objects in PyTables are
supposed to support a number of entries up to 2**62. In fact, this kind
of support is mentioned in the User's Manual as the first feature in the
"Main Features" section: 

http://pytables.sourceforge.net/html-doc/usersguide1.html#section1.1

The other kind of indexation that is used on a regular basis in PyTables
is what you called "slicing" indexation (ex. table[2:300:3], i.e. a la
numarray, with the exception that negative values for steps are not
supported). This kind of index support is in PyTables from well before
0.9.

Hope I have clearified somewhat this issue,

Francesc