preallocating a cell array of strings

[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);

TIA
ct

[C T]

[Bruno Luong]

"C T" <us...@doramail.com> wrote in message <hpnjul$3vs$1...@fred.mathworks.com>...

> 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);

Generally there is no gain to preallocate elements of cell if you intend to replace them later (this situation likely happens when using cell). See this thread for more detailed discussion:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/258931

Bruno

[James Tursa]

"C T" <us...@doramail.com> wrote in message <hpnjul$3vs$1...@fred.mathworks.com>...

test = cell(m,1);
test(:) = {'test'};

This will cause each cell to share the same physical variable 'test', so not much wasted space even if m is very large. Also gets rid of the [] cells so you can use unique.

James Tursa

[David Young]

It may depend on your criteria for "better", and also I'm not sure what you mean by saying that the main thing is the call to unique, but here is one way to set up the cell array without a loop, and with the string 'test' in every cell:

[test{1:m, 1}] = deal('test');

[Jan Simon]

Dear C T!

This is much faster than the DEAL method:
test = cell(m, 1);
test(:) = {'test'};

Jan

[Loren Shure]

In article <hpnuuj$q7q$1...@fred.mathworks.com>,
matlab.T...@nMINUSsimon.de says...

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

[us]

Loren Shure <loren...@mathworks.com> wrote in message <MPG.262cf9567...@news.mathworks.com>...

> In article <hpnuuj$q7q$1...@fred.mathworks.com>,
> matlab.T...@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