[Numpy-discussion] Empty record arrays

Christopher Barker Chris.Barker@noaa....
Mon Mar 5 18:54:12 CST 2007


empty() works too, but why would you want an empty array?

 >>> import numpy as N
 >>> dt = [("name", "S30"), ("age", "i2"), ("weight", "f4")]
 >>> a = N.empty((0,), dtype=dt)
 >>> a
array([],
       dtype=[('name', '|S30'), ('age', '>i2'), ('weight', '>f4')])

-Chris

Sameer DCosta wrote:
> Hi,
> 
> I am trying to create record arrays using the numpy.rec.fromrecords.
> This function works just fine, however I am having a little trouble
> using it to create empty record arrays. If the array I start off with
> is empty and I have provided a dtype (or the names and the formats),
> then I expect rec.fromrecords to return an empty record array. However
> I just get an error.
> 
> I am using numpy version 1.0, but a quick glance at
> numpy/core/records.py in the svn repository seems to indicate that I
> will have this problem even with the svn version. Any thoughts? Thanks
> in advance.
> 
> Sameer
> 
> 
> # *********  code snippet ***********
> from numpy import *
> recs = [( 'Bill' , 31, 260.0), ( 'Fred' , 15, 145.0)]
> dt = [("name", "S30"), ("age", "i2"), ("weight", "f4")]
> 
> # Using populated array
> r = rec.fromrecords(recs, dtype=dt)
> print r.name
> 
> try:
>     # Using empty array gives an error
>     r = rec.fromrecords([], dtype=dt)
>     print r
> except IndexError:
>     print "Index Error using empty array"
> 
> # workaround
> r = array([], dtype=dt).view(recarray)
> print r.name
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-- 
Christopher Barker, Ph.D.
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