How to create a loop and store the outputs from table?

I have extracted the data from the perticular strata from the following code;

T = readtable('Dataset.xlsx');

n = length(T.Strata)

for i=1:n

if isnan(T.Strata(i))

T.Strata(i) = T.Strata(i-1);

end

end

data=T(T.Strata==3,1:end-1)

% Say: Strata 1 has one row of data, but strata 3 has two rows of data. So, if i recall the data from strata 3, it will read the whole data of strata 3 with the help of above code.

Now further, I have to calculate one more parameter whose formula is given below:

x= ∑ N1 * S1

Where N1 is the number of elements in respective strata and S is the stadard deviation of respective strata.

So, I have to create one loop, in which both the variables get its values respectively without assigning values manually. Or store the ouput according strata.

I have attached the "dataset" for reference.

[Stephen23]

None of Strata are NaN, so what is the loop actually supposed to achieve?

T = readtable('Dataset.xlsx');

Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.

any(isnan(T.Strata))

ans = logical
   0

Rather than that loop, use:

https://www.mathworks.com/help/matlab/ref/fillmissing.html

with 'previous' option.