matplotlib

Hello Tommy,

I would like to do such convertings, too, but I think there is no such fast 
way in python. I'm using the 'for statement' to iterate over a list of 
objects and save their properties into a new list. 

best regards,
Matthias

On Friday 04 May 2007 17:54, Tommy Grav wrote:
> I have some code that simplified looks like this:
>
> class cKBO(object):
> 	def __init__(cls):
> 		cls.a = 0.
> 		cls.e = 0.
>
> lines = open("test.file","r").readlines()
>
> nlist = []
> for line in lines:
> 	obj = cKBO()
> 	(a,e) = line.split
> 	obj.a = float(a)
> 	obj.e = float(e)
> 	nlist.append(obj)
>
> I would now like to plot a vs e for all the obj objects in nlist.
> how do I do that? I tried
>
> plot(nlist[:].a,nlist[:].e,'ko')
> show()
>
> but that resulted in
> raceback (most recent call last):
>    File "/Users/tgrav/Work/MyCode/Python/MOPS/ckbos.py", line 108, in ?
>      plot(nlist[:].a,nlist[:].e,'ko')
> AttributeError: 'list' object has no attribute 'a'
>
> Which is understandable. But how do I most easily convert a list of
> class
> objects into two lists of object variables?
>
> Cheers
>    Tommy
>
>
>
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Tommy Grav <tgrav@...> writes:

> I would now like to plot a vs e for all the obj objects in nlist.
> how do I do that? I tried
>
> plot(nlist[:].a,nlist[:].e,'ko')

You have a list of objects that have attributes named a and e; these
are not attributes of the list. Try

  plot([x.a for x in nlist], [x.e for x in nlist], 'ko')

-- 
Jouni K. Seppänen
http://www.iki.fi/jks

On 5/6/07, Jouni K. Sepp=E4nen <jks@...> wrote:
> Tommy Grav <tgrav@...> writes:
>
> > I would now like to plot a vs e for all the obj objects in nlist.
> > how do I do that? I tried
> >
> > plot(nlist[:].a,nlist[:].e,'ko')
>
> You have a list of objects that have attributes named a and e; these
> are not attributes of the list. Try
>
>   plot([x.a for x in nlist], [x.e for x in nlist], 'ko')

Another idiom which I use a lot

  a,e =3D zip(*[(o.a, o.e) for o in nlist])

or if I have a lot of attributes I want dumped into arrays

  a,b,c,d =3D map(numpy.asarray, zip(*[(o.a, o.b, o.c, o.d) for o in data])=
)

JDH