Creating a matrix of blank spaces.

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Matthew Moynihan
Matthew Moynihan on 20 Jan 2011
Edited: Patrik Ek on 23 Jan 2014
If I wanted to create a matrix of blanks spaces I would use the following command:
A = [' ', ' '; ' ', ' ';];
but what if I do not know the length or width of the matrix? If the matrix was for ints or double types it would be easy:
A = zeros(column_number, row_number);
Is there a command that does the same thing as the zeros command but for characters?

Accepted Answer

Sean de Wolski
Sean de Wolski on 20 Jan 2011
You could use repmat:
repmat(' ',[3 3])
Jan on 28 Jun 2012
Accepted by JSimon
Patrik Ek
Patrik Ek on 23 Jan 2014
Edited: Patrik Ek on 23 Jan 2014
It is only so annoying that it is no constructor for char in matlab. This must be much slower than using an ordinary constructor.

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More Answers (4)

Kenneth Eaton
Kenneth Eaton on 20 Jan 2011
If you are only making a 1-D matrix (i.e. a row or column vector) then the function BLANKS is the way to go:
blankStr = blanks(4); % Makes a string of 4 blanks
For a 2-D matrix, the REPMAT-based solution from Sean de is probably the simplest, but here's another variant using the functions RESHAPE and BLANKS:
blankMat = reshape(blanks(4),2,2); % Makes a 2-by-2 matrix of blanks

Petter on 20 Jan 2011
Yet another way:
char(' '*char(ones(m,n)))

Hy on 20 Jan 2011
There is not a command for characters that is analogous to zeros. Common commands for initializing matrices of size M x N (where sz = M*N) include
The function blanks will produce a row vector. It is convenient because it avoids including a literal space character in your code, but specifying your choice of whitespace character and considering Locale Settings may produce clearer code.
Please note that because MATLAB uses column-major order [Wikipedia], I think that your example syntax should read
A = zeros(number_of_rows, number_of_columns);
The solutions by Sean and Kenneth can be restated using this syntax as:
sz = [number_of_rows, number_of_columns];
A = reshape(blanks(prod(sz)), sz);
B = repmat(' ', sz);
All of these solutions work equally well to produce arrays of dimension 1, 2, ... n.
Walter Roberson
Walter Roberson on 20 Jan 2011
I would only consider blanks() to be cleaner if it was documented as possibly using some Locale-specific horizontal whitespace, or if blanks() had options to produce Unicode whitespace characters of width em-dash or en-dash or similar use (preferably font-size relative.) But as long as blanks is confined to producing basic spaces, in my opinion using it instead of a simple literal single white space just confuses the coding.
Hy on 21 Jan 2011
Updated answer to reflect Walter's correction.

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Malcolm Lidierth
Malcolm Lidierth on 21 Jan 2011
Why is there no direct equivalent to zeros for chars? In most languages, strings are zero terminated so x=char(zeros(1,10)) may be a 10 element row vector in MATLAB's internal tables but will be perceived as a null string in most languages. Writing to a pre-allocated, but empty, char vector from a DLL or mex-file will usually crash MATLAB with a segmentation violation regardless of what numel returned in MATLAB before the call. Filling with non-zeros instead, e.g. blanks, avoids that. With short strings, my habit is to use '0123...'.



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