Counting the number of empty cells per 30 cells in excel with various lenght of data

I want to compare multiple data sets, that have different lengts. I want to extract from an excel file how many rows (with a step of 30 cells) in a single column contains text. My current code for this:

k=30;
n=29;
x2 = ending(:,a); 
[num,txt,raw] = xlsread(filename,sheet,'M2:M5710');
f_1 = 1;

for ii=1:k:x2;
    No_empty(:,f_1)=sum(~cellfun(@isempty,txt(ii:ii+n)),1);
    f_1 = f_1 + 1;

end

Here starts the problem, the x2 is different for different excel files. So I cannot store the data in a matrix.

And no I cannot add 0 to the shorter data, I use the numbers for further calculations.

I tried with cell arrays, but then I got stuck in doing further calculations and plotting. So any hint is helpful at this point.