[Numpy-discussion] Subarray with with arbitrary index?

Paul F. Dubois paul at pfdubois.com
Sat Aug 18 11:29:23 CDT 2001


I'm afraid that you have to do put using one-d indices. But you do *not*
have to try to ravel the source. I.e., the first arg is just the name of
the array.
>>> from Numeric import *
>>> x=array([[1,2,3],[4,5,6]])
>>> x
array([[1, 2, 3],
       [4, 5, 6]])
>>> put(x,[0,4],[100,200])
>>> x
array([[100,   2,   3],
       [  4, 200,   6]])
>>>
-----Original Message-----
From: Huaiyu Zhu [mailto:huaiyu_zhu at yahoo.com] 
Sent: Friday, August 17, 2001 11:36 PM
To: Paul F. Dubois
Cc: John J. Lee
Subject: RE: [Numpy-discussion] Subarray with with arbitrary index?

Thanks, John and Paul.  That is what I was looking for.

It did not occur to me to look for verbs put and take, rather than words
line sub- index, slice and so on.  Maybe puting some of these words in
the manual could help people doing a search?

Now that this made the most costly part of my program about seven times
faster, other problems become more prominent.  One of such question is:
How do we do it on more than one axis?

Suppose a is a 2d array. Then put(a[1,:], b, c) works, but put(a[:,1],
b,
c) complains about the first argument not a continuous array.  Doing
transpose does not help.  So do I guess it right that this is
implemented
only in the representation of a linear array?

If so, there would be no hope of using put(a, ([2, 4], [1,2]), v) or
even
more exotic ones like using += on an arbitray subgrid?

Regards,

Huaiyu

On Fri, 17 Aug 2001, Paul F. Dubois wrote:

> John is right:
> >>> a=Numeric.arange(8)
> >>> b=Numeric.array([2,3,5])
> >>> c=Numeric.arange(3)+100
> >>> Numeric.put(a,b,c)
> >>> print a
> [  0   1 100 101   4 102   6   7]
> 
> Thanks for pointing out that I had left allclose out of the Numeric
part of
> the manual. I did it in the MA part and then forgot. I'm fixing it
now. BTW:
> There are changenotes at source forge that are sometimes ahead of the
> manual.
> 
> -----Original Message-----
> From: numpy-discussion-admin at lists.sourceforge.net
> [mailto:numpy-discussion-admin at lists.sourceforge.net]On Behalf Of John
> J. Lee
> Sent: Friday, August 17, 2001 6:36 AM
> To: Huaiyu Zhu
> Cc: numpy-discussion at lists.sourceforge.net
> Subject: Re: [Numpy-discussion] Subarray with with arbitrary index?
> 
> 
> On Thu, 16 Aug 2001, Huaiyu Zhu wrote:
> 
> > Hi,
> >
> > Is it possible to assign to a subarray with arbitrary index?
> >
> > Suppose I have three arrays
> >
> > a = arange(8)
> > b = array([2, 3, 5])
> > c = arange(3)+100
> >
> > I want a function f, such that calling  f(a, b, c) would change a to
> >
> > [0 1 100 101 4 102 6 7]
> 
> f = Numeric.put
> f(a, b, c)
> 
> put used to be in Python, but it's been in C since some release
17.x.x, I
> think.
> 
> I have a sinking feeling that I must have missed something (no
interpreter
> here to check it works)...
> 
> BTW, a week ago I noticed that I had reinvented the wheel in
rewriting, in
> an uglier and less efficient form, Numeric.allclose (hope I got the
name
> right).  As far as I can see, it isn't listed in the manual.  Did I
miss
> it?  All it would need is the docstring copying over.
> 
> 
> John
> 
> 
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