Achieve Matlab's `num2str` behaviour in Octave

Question

The following code

x = [1.1, 2.22, -3.3; 4.44, 5.55, 6.6];
fmt = '%.16g ';
y = num2str(x, fmt)

produces different results in Matlab (R20105b)

y =
 1.1 2.22 -3.3
4.44 5.55  6.6

and in Octave (4.0.0)

y =
1.1 2.22 -3.3
4.44 5.55 6.6

The difference is the alignment: in Matlab the columns are right-aligned, whereas in Octave they are not aligned.

I'd like to achieve exactly Matlab's behaviour in Octave. Do you know any solution for this? Of course I could write my own function, but maybe there already exists a solution.

EDIT

Another difference is how multidimensional arrays are treated. For example,

x = cat(3, magic(3), -magic(3));
fmt = '%.16g ';
y = num2str(x, fmt)

produces in Matlab

y =
8  1  6 -8 -1 -6
3  5  7 -3 -5 -7
4  9  2 -4 -9 -2

and in Octave

y =

8 1 6
3 5 7
4 9 2
-8 -1 -6
-3 -5 -7
-4 -9 -2

That is, Matlab attaches the 3D slices along the second dimension, and Octave along the first.

Answer 1

This is more of a workaround than a solution; and I'm not totally satisfied with it. But here it goes. If anyone has a better or more general solution please tell.

The following only works for a single formatting operator, as in the example (it doesn't work for something like fmt = '%.2f %.1f'), and only for real (not complex) numbers. It works for arrays with more than 2 dimensions, mimicking Matlab's behaviour: it collapses all dimensions beyond the first into a single (second) dimension.

if ischar(x)
    y = x;
else
    y = sprintf([fmt '\n'], reshape(x,size(x,1),[]).'); %'// each row of y is a string.
                                                        % // '\n' is used as separator
    y = regexp(y, '\n', 'split'); %// separate
    y = y(1:end-1).'; %'// remove last '\n'
    y = cellfun(@fliplr, y, 'uniformoutput', false); %// invert each string
    y = char(y); %// concatenate the strings vertically. This aligns to the left
    y = fliplr(y); %// invert back to get right alignment
    y = reshape(y.',[],size(x,1)).'; %// reshape into the shape of x
    y = strtrim(y); %// remove leading and trailing space, like num2str does
end

This produces, both in Matlab in Octave, the same result as produced by y = num2str(x, fmt) in Matlab.

It should be noted that when the first input is a char array num2str ignores the second input (format specifier) and produces as output the same char array, both in Matlab and in Octave. Thus num2str('abc', '%f ') produces 'abc'. However, sprintf works differently: it forces the use of the format specifier, interpreting the chars of the input as ASCII codes if needed. That's why the if branch is needed in the above code.