MATLAB: Separate string with tag_string

MATLABseparate long string

Dear bros,
I want to separate long string which contains tags to each classify.
Example: 
string = 'tag_A(this is tag A, it contains tag_B(this is tag_B, it contains tag_C(figure.png). This is still tag B). This is still tag A)';
output is array string or cell array such as:
this is tag A, it contains tag_B      tag_A
this is tag_B, it contains tag_C      tag_B
figure.png  		              tag_C
This is still tag           	      tag_B
This is still tag A 	              tag_A
I used strfind, regexp, etc. but it does not work.
Do any one can help me?
Thank you so much

Best Answer

This should get you started. Adjust as required.
str = 'tag_A(this is tag A, it contains tag_B(this is tag_B, it contains tag_C(figure.png). This is still tag B). This is still tag A)';
abc = cell(0,2);
xyz = cell(0,2);
rgx = '(\w+)\((.+)\)';
tkn = regexp(str,rgx,'once','tokens');
while numel(tkn)
    tag = tkn{1};
    [tkn,spl] = regexp(tkn{2},rgx,'once','tokens','split');
    abc = [abc;spl(1),tag];   %#ok<AGROW>

    xyz = [spl(end),tag;xyz]; %#ok<AGROW>
end
out = [abc;xyz(2:end,:)]
giving:
out = 
    'this is tag A, it contains '    'tag_A'
    'this is tag_B, it contains '    'tag_B'
    'figure.png'                     'tag_C'
    '. This is still tag B'          'tag_B'
    '. This is still tag A'          'tag_A'
Note that regular expressions cannot easily match arbitrarily-nested pairs of parentheses. This answer will only work for input strings with nested parentheses, i.e. (...(...)...), as your example shows. It will not work for multiple parenthesis pairs on the same level of nesting, i.e. (...)(...).
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