how to create a 1,12,123,1234 pattern in a triangle

How do I make a pattern from 1:N, Lets say N = 5, so it turns out like this:

1

12

123

1234

12345

Answer 1

[Guillaume]

Use a loop or

n = 5;
c = arrayfun(@(nn) 1:nn, (1:n)', 'UniformOutput', false);
celldisp(c)

You obviously can't store the result in a matrix since matrices are square by definition.

[ali b]

Thanks for your answer, any chance it could be done using a loop?

[Guillaume]

Yes, just replace the arrayfun by a loop:

c = cell(1, n);
for nn = 1:n
   c{nn} = 1:nn;
end

Answer 2

[Image Analyst]

If you want a simple "for" loop way of printing this to the command window, try this:

N = 5
for k = 1 : N
  % Print this line in the command window.
  fprintf('%d ', 1:k);
  % Scroll down to the next line.
  fprintf('\n'); 
end

[Mikaila Denise Loanzon]

I tried your code and it worked. How about if I wanted the output to look like this?

n = 4

1

12

123

1234

Thank you!

[Les Beckham]

Try this:

N = 5
fmt = sprintf('%%%dd', N); % format to print right-justified with N characters width
for k = 1 : N
    str = sprintf('%d', 1:k); % numbers 1 through k as a string
    % Print this line in the command window.
    fprintf(fmt, str2num(str));
    % Scroll down to the next line.
    fprintf('\n'); 
end

[Image Analyst]

Try this:

fprintf('n = 4\n'); % Print the n=4 line.
vec = [1,12,123,1234]; % Some data...
for k = 1 : length(vec)
  % Print a space followed by a field of 4 for the number.
  fprintf(' %4d\n', vec(k));
end

n = 4

1

12

123

1234

[DGM]

Why not go one step further?

fprintf('n = 4\n'); % print a fake assignment echo

n = 4

vec = {'   1','  12',' 123','1234'}; % if we're going to precalculate results ...
fprintf('%s\n',vec{:}); % homework complete!

   1
  12
 123
1234

No wait!

result = 'n = 4\n   1\n  12\n 123\n1234\n';
fprintf(result); % that was way easier!

n = 4
   1
  12
 123
1234

Answer 3

[Azzi Abdelmalek]

n=5
out=arrayfun(@(x) str2num('1':num2str(x)),1:n)'

[Guillaume]

It's clever but this will only work for n up to 9

Answer 4

[DGM]

I know this is not the only one of these threads, but I'm just going to throw this here anyway. Since I don't really care about meeting unspecified requirements of junk homework, I choose to assume my own.

I want to support n>9; in order to facilitate that, we need to prevent ambiguity by adding spaces between numbers. I choose to assume that formatting is based on a fixed field width instead of a fixed inter-field pad width. I also want to support both right and left justification of the overall line, but within each internal field, the numbers should always be right-justified. Lastly, since I think the point of this exercise is basic string formatting, I don't want to rely on the output behavior of celldisp() or similar; likewise, I don't want a bunch of array indices or other chaff printed between each output line.

Here's what I have. I'm not great with wringing elegance out of fprintf(), but it does what I expected it to do.

% n,minpad both must be positive nonzero integers
triprint(20,1,'left')

 1
 1  2
 1  2  3
 1  2  3  4
 1  2  3  4  5
 1  2  3  4  5  6
 1  2  3  4  5  6  7
 1  2  3  4  5  6  7  8
 1  2  3  4  5  6  7  8  9
 1  2  3  4  5  6  7  8  9 10
 1  2  3  4  5  6  7  8  9 10 11
 1  2  3  4  5  6  7  8  9 10 11 12
 1  2  3  4  5  6  7  8  9 10 11 12 13
 1  2  3  4  5  6  7  8  9 10 11 12 13 14
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20

triprint(20,1,'right')

                                                          1
                                                       1  2
                                                    1  2  3
                                                 1  2  3  4
                                              1  2  3  4  5
                                           1  2  3  4  5  6
                                        1  2  3  4  5  6  7
                                     1  2  3  4  5  6  7  8
                                  1  2  3  4  5  6  7  8  9
                               1  2  3  4  5  6  7  8  9 10
                            1  2  3  4  5  6  7  8  9 10 11
                         1  2  3  4  5  6  7  8  9 10 11 12
                      1  2  3  4  5  6  7  8  9 10 11 12 13
                   1  2  3  4  5  6  7  8  9 10 11 12 13 14
                1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
             1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16
          1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17
       1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18
    1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19
 1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20

function triprint(n,minpad,justify)
% synopsis goes here ...

    % validate inputs or provide defaults ...
    
    % calculate the internal field format expression
    ifw = max(ceil(log10(abs(double(fix(1:n)))+1))) + minpad; % field width
    ifmt = sprintf('%%%dd',ifw); % always right-justified 
    
    for k = 1:n
        rowstr = sprintf(ifmt,1:k); % block of right-justified fixed-width number fields
        switch lower(justify)
            case 'right'
                strpad = repmat(' ',1,ifw*n - numel(rowstr)); % block of spaces
                fprintf('%s%s\n',strpad,rowstr(minpad+1:end)); % print both, stripping leading pad        
            case 'left'
                % no point adding trailing pad blocks
                fprintf('%s\n',rowstr(minpad+1:end)); % print it, stripping leading pad            
            otherwise
                error('this is an error message')
        end
    end
end