A Saturday 04 October 2008, Mico Filós escrigué:
> Hi,
>
> I am trying to use pytables to store simulated data. The data
> organizes quite stereotypically:
>
> 1. I have a set of parameters, say A, B, and C, which take different
> values, e.g,
>
>         A = {a1, a2, a3},    B = {b1, b2},    and  C = {c1, c2, c3, 
> c4}
>
> 2. For each combination of values for A, B, and C, I have a
> collection of datasets corresponding
>    to different "observations" of the same process:
>
>          {A = a1, B = b1, C = c1:     observation1, observation2,
> ...}, {A = a2, B = b1, C = c1:     observation1, observation2, ...},
> etc.
>
> 3. Each 'observation' consists of a table,  whose fields are 'time'
> and x1, x2, x3 ...  (the different variables of the system).
>    The number of rows of this table is not necessarily the same for
> all observations.
>
> I have read the documentation,  but I cannot figure out the best way
> to organize these data.
> A first, naïve guess would be a table like this
>
> A      B      C      data
> ---------------------------
> a1    b1    c1    Table1
> a2    b1    c1    Table2, etc
>
> where each *entry* in the field 'data' consists, in turn, of another
> table, with fields
>
> ntrial   trajectory
> ---------------------
> 1         traj_array1
> 2         traj_array2, etc.
>
> Each entry in the the field 'trajectory' is an array (or, perhaps,
> another table).
> But I am not sure if this can be done.
>
> I would truly appreciate any help on this.

You can only include variable-length objects in the VLArray object.  
With this, my advice is to save the parameters (fixed-length records) 
in a Table object and the observations (variable-length records) in a 
VLArray.  For the latter you can use a multidimensional regular Atom in 
case your observations have an homogeneous type.  In case of 
observations with a heterogeneous type, you may use an ObjectAtom 
(although pickle/unpickle will be used under the hood).

Hope that helps,

-- 
Francesc Alted
Freelance developer
Tel +34-964-282-249

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