Extracting numbers using Regex in Matlab-CodePudding

I would like to extract integers from strings from a cell array in Matlab. Each string contains 1 or 2 integers formatted as shown below. Each number can be one or two digits. I would like to convert each string to a 1x2 array. If there is only one number in the string, the second column should be -1. If there are two numbers then the first entry should be the first number, and the second entry should be the second number.

'[1, 2]'
'[3]'
'[10, 3]'
'[1, 12]'
'[11, 12]'

Thank you very much!

I have tried a few different methods that did not work out. I think that I need to use regex and am having difficulty finding the proper expression.

CodePudding user response：

You can use str2num to convert well formatted chars (which you appear to have) to the correct arrays/scalars. Then simply pad from the end 1 element to the 2nd element (note this is nothing in the case there's already two elements) with the value -1.

This is most clearly done in a small loop, see the comments for details:

% Set up the input
c = { ...
    '[1, 2]'
    '[3]'
    '[10, 3]'
    '[1, 12]'
    '[11, 12]'
    };

n = cell(size(c));          % Initialise output
for ii = 1:numel(n)         % Loop over chars in 'c'
    n{ii} = str2num(c{ii}); % convert char to numeric array
    n{ii}(end 1:2) = -1;    % Extend (if needed) to 2 elements = -1
end

% (Optional) Convert from a cell to an Nx2 array
n = cell2mat(n);

If you really wanted to use regex, you could replace the loop part with something similar:

n = regexp( c, '\d{1,2}', 'match' ); % Match between one and two digits
for ii = 1:numel(n)
    n{ii} = str2double(n{ii});       % Convert cellstr of chars to arrays
    n{ii}(end 1:2) = -1;             % Pad to be at least 2 elements
end

But there are lots of ways to do this without touching regex, for example you could erase the square brackets, split on a comma, and pad with -1 according to whether or not there's a comma in each row. Wrap it all in a much harder to read (vs a loop) cellfun and ta-dah you get a one-liner:

n = cellfun( @(x) [str2double( strsplit( erase(x,{'[',']'}), ',' ) ), -1*ones(1,1-nnz(x==','))], c, 'uni', 0 );

I'd recommend one of the loops for ease of reading and debugging.