How to add some symbols into a matrix ?

In fact , I have a Matrix like X =

0 5.2 4.8 28.8

0 0 1.0 33.8

0 0 0 33.4

0 0 0 0

I would like to create like this

0 5.2 4.8 28.8

NaN 0 1.08 33.8

NaN NaN 0 33.4

NaN NaN NaN 0

I wrote something like this, but it does not work very well. because I would like to keep the first column and first row zero value, the second column second row zero value and so on

[m,n]=size (X) for i=1:m; for j=1:n; if X(i,j)==0 X(i,j)= NaN ; end end end

Answer 1

[Daniel Shub]

It depends on what you want to do with this matrix. If you just want it to be displayed nicely:

classdef partmat < double
  methods
    function obj = partmat(data)
      if nargin < 1
        data = [];
      end
      validateattributes(data, {'numeric'}, {'2d'})
      obj = obj@double(data);
    end
    
    function disp(obj)
      for irow = 1:size(obj, 1)
        for icolumn = 1:size(obj, 2)
          if ~isnan(obj(irow, icolumn))
            x = num2str(obj(irow, icolumn));
          else
            x = '--';
          end
          fprintf(['\t', x]);
        end
        fprintf('\n');
      end
    end
  end
end

Example:

>> x = partmat(magic(5))

x =

17 24 1 8 15

23 5 7 14 16

4 6 13 20 22

10 12 19 21 3

11 18 25 2 9

>> x(3) = nan

x =

17 24 1 8 15

23 5 7 14 16

-- 6 13 20 22

10 12 19 21 3

11 18 25 2 9

If you want to get even fancier you could overload subsassgn and allow notation like

x(5) = '--'

[Niki]

what do you mean of classdef partmat < double?

i got error

Error: Illegal use of reserved keyword "classdef".

[Daniel Shub]

What version of MATLAB are you using? The code needs to be saved into a file called partmat.m.

[Niki]

I have all these versions 6.5 7.1 7.9 and 7.12

Answer 2

[Andrei Bobrov]

X(tril(true(size(X)),-1))=nan

add

X(bsxfun(@lt,1:4,(1:4)'))=nan

more

only for cell array

Xc = num2cell(X)
Xc(bsxfun(@lt,1:4,(1:4)'))={'-'}

[Niki]

Thanks for your prompt reply, if I would like to add something else like - symbol, then what should I do ?

[Walter Roberson]

text symbols cannot appear in numeric matrices. If you want a number prefixed by "-" then probably the easiest way to do that is to multiply the number by negative 1. But it looks to me like perhaps you want an n-dash rather than a minus sign.

[Andrei Bobrov]

I agree with Walter Robenson

[Niki]

In fact both andrei answer are very nice and useful,

Walter no, I do not want to prefix a number by "-",

I just wanted to put "-" instead zero when I copied the output into a xls file

However it seems that Andrei second comment works well .

I put another question , please also take a look at it