Creating a cell array of size n

I need a cell array of size n, like if n is 3, I need

 C = {'red','red','red'}

If n is 100,

 C = {'red','red',.......'red'}(100 cells)

I tried this,

C = cell(1,n);
 for i = 1:n
   C(i) = 'red';
 end

This gives known error of conversion to cell from char is not possible.

Answer 1

[James Tursa]

The most memory efficient way is the following without a loop:

C(1:n) = {'red'}; % Assuming C doesn't exist yet (EDITED)

That is because in the above line, all n copies of the 'red' string are reference copies of each other (like a shared data copy), so the memory footprint is smaller than filling each cell individually with a brand new allocated string in a loop.

Having said that, I strongly suspect that what you are attempting to do is futile. If you change any of the individual 'red' strings downstream in your code you will probably need to allocate brand new cell element variables anyway, so this pre-allocation of 'red' would be useless (actually wastes time) regardless of the methoud you use to create C in the first place (my method or with a loop). The only exceptions would be if you don't plan on altering C at all downstream, or if you plan to operate on each string "in-place" ... i.e., changing the contents of the string directly without changing its length, etc. Can you elaborate on what you intend to do with C downstream in your code?

[Kye Taylor]

The command C(1,n) = {'red} only assigns the cell {'red'} to the nth element of C. The jth elements (for j < n) are empty arrays... NOT referenced copies of the nth element.

[James Tursa]

My typo. Should have been:

C(1:n) = {'red'}

I have edited my original post. All of my original comments still apply.

[Albert Yam]

See Jan Simon's answer. James just missed a '1:n'.

C(1,1:n) = {'red'};

[James Tursa]

P.S. My comments also apply to Jan's answer, since it essentially does the same thing.

Answer 2

[Jan]

C = cell(1, n);
C(:) = {'red'};

Answer 3

[F.]

Your error :

C(i) = 'red';

C is a cell array, with C(i) you reach the place in the cell array and not the element which is in this place. So try :

C{i} = 'red';

[F.]

I'm not sure but try also this :

   n = 100
   repmat( {'red'}, 1, n )

[Giuseppe Degan Di Dieco]

Dear F,

thanks for your explanation of the cell array object.

Actually, it was quite tricky to understand.

Best.

Answer 4

[grapevine]

You have to modify your code in this way :

     C = cell(1,n);
     for i = 1:n
       C(i) = java.lang.String('red');
     end

http://www.mathworks.nl/help/techdoc/ref/cell.html

Another solution could pass by using the function: char2cell, which is available on Matlab Central Exchange

http://www.mathworks.com/matlabcentral/fileexchange/24915-char2cell

good luck

[Jan]

java.lang.String ?! Why should this be converted to a java string? And CHAR2CELL seems not helpful also.

[grapevine]

Weird! it works for me. read the doc :)