Error using function regexp

Problem: in this code I want to obtain postfixes of semanticTrajCompact.Trajcompact; after I want count the combination of values 0-5 in them. I'm not able to solve why the function 'regexp' generates the error 'Error using regexp. All cells must be strings.'

for k=1:25
  [matches(:,k), postfix(:,k)] = regexp(semanticTrajCompact(1,4).TrajCompact,sprintf('%d%d(.*)',digits{1}(k),digits{2}(k)),'match','once','tokens');
end
postfix(cellfun(@isempty,postfix)) = {''};
for k=1:25
    matchcount = cell(size(digits{1}));
    if ~isempty(postfix)
        for i = 1:numel(matchcount)
            matchstart = regexp(postfix, sprintf('%d.+?%d', digits{1}(k), digits{2}(k)));
            matchcount{i} = cellfun(@numel,matchstart);
        end
    end
end

for idx=1:numel(matchcount)
      matchcount{idx}=permute(matchcount{idx},[3,2,1]);
end

      matchcount=cell2mat(matchcount);
      valueNoZero=(matchcount~=0);
      counter=sum(valueNoZero(:,:,:),3);

Postfix is a cell array 93% empty. How can I solve the problem? Maybe I need to filter out the non-string cells before passing them to regexp. But I don't know to filter out the non string cells and at the same time have the same structure of postfix [nx25]... I have tried horzcat/vertcat but this function put all values in the same vector.

[Adam]

cellfun( @ischar, postfix )

will tell you which elements of your array are not strings.

postfix(cellfun(@isempty,postfix)) = {''};

in your code should have dealt with all the cases of empty cells and turned them into strings.

Answer 1

[Sean de Wolski]

iscellstr(C)

Has to return true. The following should remove empty or non-character elements from the cell.

C = C(cellfun(@ischar,C));