How to select the specific rows that I want in matrix using for loop?

I have 150 X 344 matrix, 150 is the file numbers that I need to examine and 344 is my total number of features ('CombineFeatureAll'). I want to undergo 1-50 rows for testing and another 51-150 rows for training. Inside the 1-50 rows, the number smaller than 25 will be 1 else -1. I know by coding like this size(CombineFeatureAll,1) will get all the rows, but how can I limit it to only 50 rows? Below is my coding for testing part.

%start
for c2 = 1:size(CombineFeatureAll,1)
%for label
  if c2<=25
    str1=['1' ' '];
  else
    str1=['-1' ' '];
  end
  for c1 = 1:size(CombineFeatureAll,2)
    str1 =[str1 ['',num2str(c1),':' num2str(CombineFeatureAll(c2,c1)) ' '] ];%feature set
   end
   dlmwrite('testing.te', str1, 'delimiter', '', 'precision', 6,'-append');
end

[Adam]

What do you actually want the output to be?

Answer 1

[ai ping Ng]

A = CombineFeatureAll(1:50,1:344);

for c2 = 1:size(A,1)

      %for label
      if c2<=25
          str1=['1' ' '];
      else 
          str1=['-1' ' '];
      end

      for c1 = 1:size(A,2)
          str1 =[str1 ['',num2str(c1),':' num2str(A(c2,c1)) ' '] ];%feature set
      end

      dlmwrite('testing.te', str1, 'delimiter', '', 'precision', 6,'-append');
  end

It can be run this way but this maybe not a good method?

Answer 2

[Walter Roberson]

A = CombineFeatureAll(1:50,1:344);
c2 = [ones(25,1); -ones(25,1)];
t = [c2, A];
dlmwrite('testing.te', A, 'precision', 6);