From octave-sources-request at bevo dot che dot wisc dot edu  Wed Jun  6 01:43:43 2001
Subject: Re: Cell array support
From: Paul Kienzle <pkienzle at kienzle dot powernet dot co dot uk>
To: Jianming <caijianming at yahoo dot co dot uk>
Cc: octave-sources <octave-sources at bevo dot che dot wisc dot edu>,         "John W. Eaton" <jwe@bevo.che.wisc.edu>
Date: Wed, 6 Jun 2001 07:43:32 +0100

On Wed, Jun 06, 2001 at 09:31:52AM +0800, Jianming wrote:
> Hi,
>     I hope you have seen my recent cell array patch on octave-sources. Here
> are some more thoughts I have when digging through octave code, trying to
> implement more cell functions.
> 
> > IMHO, "x(idx) = []" for deletion is already pretty arbitrary (shouldn't it
> > produce a dimension conflict?), so I don't put too weight on consistency.
> >
> > I would be happier if deletion was identified in the parser, rather
> > than relying on the semantics of assignment from a particular value.
> > Something like "clear x(idx)" would be even less confusing.  And less
> > error prone: consider "x(j) = b" where you are expecting a scalar b,
> > but someone passed b as [] instead.  However, interpreting assignment
> > from and empty matrix as deletion of the indexed values is the defacto
> > standard, at least in Matlab, RLaB, SciLab and Octave.
> 
> The assignment to empty values causes deletion at the underlying Array and
> Array2 classes. For matrix, empty values are []. For octave, empty values
> are {}. That is way the deletion cellvar(idx)={}will require no addtional
> work for the parser, and indeed for the intermediate classes, which is quite
> convienent and clean. Hence, I would not recommand special code to perform
> cellvar(idx)=[]. However, for consistency with Matlab etc, I guess we can
> create a special variable called maybe DELCELL. In octave, DELCELL={}, in
> Matlab etc DELCELL=[]. Hence, the users would use cellvar(idx)=DELCELL, and
> porting would not be a problem.

The following bit of code gives an array dimension mismatch error in matlab,
so your idea won't work.

	y=[];
	x(I) = y;

Paul Kienzle
pkienzle at users dot sf dot net



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