[Numpy-discussion] PyTables, array and recarray

Hanno Klemm klemm@phys.ethz...
Fri May 30 10:17:18 CDT 2008


Hi,

I try to save the contents of a numpy recarray with PyTables into a
file. That works well, however, if I then try to retrieve the data, I
get back an array with matching dtypes rather than a recarray.

What is the best way to get a recarray back, or if that's not possible
what's the most efficient way to convert an array to a recarray? 

This is what I am doing at the moment:
 
Python 2.5 (r25:51908, Oct  4 2006, 17:28:51)
[GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-52)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as N
>>> import tables as t
>>> num = 2
>>> a = N.recarray(num, formats='i4,f8,f8',names='id,x,y')
>>> a['id'] = [3,4]
>>> a['x'] = [3.4,4.5]
>>> a['y'] = [4.6,4.5]
>>> a
recarray([(3, 3.3999999999999999, 4.5999999999999996), (4, 4.5, 4.5)],
      dtype=[('id', '<i4'), ('x', '<f8'), ('y', '<f8')])
>>> f = t.openFile('test.h5', 'w')
>>> f.createTable('/', 'test', a)
/test (Table(2L,)) ''
  description := {
  "id": Int32Col(shape=(), dflt=0, pos=0),
  "x": Float64Col(shape=(), dflt=0.0, pos=1),
  "y": Float64Col(shape=(), dflt=0.0, pos=2)}
  byteorder := 'little'
  chunkshape := (409,)
>>> f.close()
>>> f = t.openFile('test.h5', 'r')
>>> b = f.root.test[:]
>>> b
array([(3, 3.3999999999999999, 4.5999999999999996), (4, 4.5, 4.5)],
      dtype=[('id', '<i4'), ('x', '<f8'), ('y', '<f8')])
>>> type(b)
<type 'numpy.ndarray'>
>>> type(a)
<class 'numpy.core.records.recarray'>
>>>

Best regards,
Hanno

-- 
Hanno Klemm
klemm@phys.ethz.ch




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