Creating a matrix of blank spaces.

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?

Answer 1

[Sean de Wolski]

You could use repmat:

repmat(' ',[3 3])

[Paulo Silva]

char(double(' ')*ones(3,3))

[Ned Gulley]

Paulo, that's a good answer. You should add it as another answer (rather than as a comment) so that it can earn votes and perhaps get it accepted by the question's author.

[Paulo Silva]

Hi Ned, my answer isn't that good, Sean code is faster and simpler than mine, it was just to give another alternative :)

[Walter Roberson]

Or mildly faster but more obscure than repmat would be

blank = '';

blank(ones(column_number,row_number))

This is what repmat will end up doing internally.

[Walter Roberson]

Paulo, the double() is not needed:

char(' ' * ones(column_number,row_number))

[Walter Roberson]

Also,

char(' ' + zeros(column_number,row_number))

[Jan]

Accepted by JSimon

[Patrik Ek]

It is only so annoying that it is no constructor for char in matlab. This must be much slower than using an ordinary constructor.

Answer 2

[Kenneth Eaton]

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

Answer 3

[Petter]

Yet another way:

char(' '*char(ones(m,n)))

[Walter Roberson]

The inner char() is not needed.

Answer 4

[Hy]

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

• those for doubles and singles: zeros(sz), ones(sz), nan(sz), inf(sz)
• those for logicals: true(sz), false(sz)
• those for cells: cell(sz)

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);
 display(isequal(A,B));

All of these solutions work equally well to produce arrays of dimension 1, 2, ... n.

[Walter Roberson]

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]

Updated answer to reflect Walter's correction.

Answer 5

[Malcolm Lidierth]

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...'.