Reading multiple text files with two columns in MATLAB - matlab

Question

I want to read multiple text files. Each text file has two columns. All the two columns of all text files have same rows. I want to know, in MATLAB, how to read each text file then read each column one by one, subtract one column data from the other column and then read the next file and so on. I have written the following code but I am missing some step in the code. I appreciate your support. Thank you all.
for k = 1:9
filename = sprintf('Data_F_Ind000%d.txt',k);
a(:,k) = load(filename);
x = a(:,1)};
y = a(:,2);
z = x - y;
end

Answer 1

data = cell(9,1) ;
diff_data = cell(9,1) ;
for k = 1:9
filename = sprintf('Data_F_Ind000%d.txt',k);
a = load(filename);
data{i} = a ;
x = a(:,1)};
y = a(:,2);
diff_data{i} = x - y;
end

Answer 2

You can do this multiple ways. I imagine that you want to do something with z instead of just throwing it away every time. I would do this by taking advantage of an access pattern.
numFiles = 9;
numRows = ....; % not required but used to preallocate the a matrix
pattern = 1:2:numFiles * 2; % create a vector of 1 3 5 ...
a = zeros(numRows, numFiles * 2);
z = zeros(numRows, numFiles);
for k = 1:numFiles
fileName = sprintf('Data_F_Ind000%d.txt, 'k');
a(:,pattern(k):pattern(k) + 1) = load(fileName);
z(:,k) = a(:,pattern(k)) - a(:,pattern(k) + 1);
end
This is untested and is clearly missing some data but the intent should be clear. You don't need to preallocate variables but it helps speed calculations so I try to do it whenever possible.