[SciPy-User] Populating a recarray from 0 size

Sergi Pons Freixes spons@utm.csic...
Sun Aug 22 13:23:43 CDT 2010


On Sat, Aug 21, 2010 at 6:29 PM,  <josef.pktd@gmail.com> wrote:
> BTW: These are numpy functions.

Oh, sorry, I am so used to call numpy functions via scipy that I
forgot about it.

>
> I don't know the answer, but it would be more efficient to correctly
> size the empty array, if you know the size, or to build up the array
> first as a list of tuples before converting to an array.

The problem is that the size is not known. I'll think about the list of tuples.


On Sun, Aug 22, 2010 at 8:19 AM, Åsmund Hjulstad
<asmund.hjulstad@gmail.com> wrote:
>
>
> My approach in this kind of situation has been using pytables, creating an
> empty table with a specific dtype, and then populating the table with the
> append method. It seems very efficient, and quite convenient in situations
> where I eventually will need to persist data to disk somehow.
> Reading the table into an in memory recarray is then easily done using
> data = h5file.root.datatable[:].view(numpy.recarray)
>

Mmm, it sounds a bit overkill to use pytables just for having a
recarray with dynamic size. Anyway, I'll have a look at it, thank you.


I would also appreciate is a reasoning of why is scipy.resize (e.g.,
numpy.resize) raising this exception. The idea increasing the size of
a 0-size array doesn't sound very weird to me, so I was shocked that i
wasn't working. Actually, I've been successfully using the method
array.resize(newsize) previously, but now I'm "forced" to use
scipy.resize because of the "ValueError: cannot resize an array that
has been referenced or is referencing another array in this way."
issue (see [1]).

If this conversation is more appropriate to be developed in the numpy
mailing list, please let me now and I will migrate it.

Regards,
Sergi

[1] http://www.scipy.org/Numpy_Example_List#head-d5585278b02f43f78eb75a4fdc337fdc12417426


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