preallocating a cell array of strings

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From: Loren Shure on 12 Apr 2010 10:33

---

In article <hpnuuj$q7q$1(a)fred.mathworks.com>,
matlab.THIS_YEAR(a)nMINUSsimon.de says...
> Dear C T!
>
> > I am trying to pre-allocate a cell array of strings. I can do the following:
> >
> > test = cell(m,1);
> > for i = 1:m
> > test{i} = 'test';
> > end;
> > unique(test);
> >
> > But I thought there may be a better solution somewhere. The main thing is being able to do unique(test);
>
> This is much faster than the DEAL method:
> test = cell(m, 1);
> test(:) = {'test'};
>
> Jan
>

I haven't looked, but I bet the test(:) = {'test'} uses a shared data
copy for the string value, whereas the deal version might not. So part
of the difference might be the extra real memory allocation going on.
Just a guess though.

--
Loren
http://blogs.mathworks.com/loren
http://matlabwiki.mathworks.com/MATLAB_FAQ

From: us on 12 Apr 2010 10:46

---

Loren Shure <loren.shure(a)mathworks.com> wrote in message <MPG.262cf95677fa13be989ada(a)news.mathworks.com>...
> In article <hpnuuj$q7q$1(a)fred.mathworks.com>,
> matlab.THIS_YEAR(a)nMINUSsimon.de says...
> > Dear C T!
> >
> > > I am trying to pre-allocate a cell array of strings. I can do the following:
> > >
> > > test = cell(m,1);
> > > for i = 1:m
> > > test{i} = 'test';
> > > end;
> > > unique(test);
> > >
> > > But I thought there may be a better solution somewhere. The main thing is being able to do unique(test);
> >
> > This is much faster than the DEAL method:
> > test = cell(m, 1);
> > test(:) = {'test'};
> >
> > Jan
> >
>
> I haven't looked, but I bet the test(:) = {'test'} uses a shared data
> copy for the string value, whereas the deal version might not. So part
> of the difference might be the extra real memory allocation going on.
> Just a guess though.

loren
actually, DEAL is using a shared copy...
something along this line has been discussed several times in CSSM, eg,

http://www.mathworks.com/matlabcentral/newsreader/view_thread/146789#369303

urs

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