Delete every n rows if less than x

Hi I have a m x 14 matrix. I want to consider the first 24 rows. If the value in coulmn 5 in row 14 is less than x, then delete the first 24 rows. I want to repeat this for the rest of the matrix as well, considering 24 rows at a time

[Rik]

What have you tried? This seems a perfect job for a while loop.

(Or use a for loop to loop backwards through the elements)

[David du Preez]

I'm not really sure where to start even

[Jan]

@David: Please give us any useful details. Did you read the "Getting Started" chapters of the documentation already? Did you see Matlab's Onramp tutorials? Is m a multiple of 24? Do you know how to create a FOR loop?

[David du Preez]

@Jan: Yes m is a multiple of 24. The matrix contains hourly values. Column 1 contains datenum values. Therefore row 14 column 5 will be the daily 13:00 value. Will have a look at the tutorial now

Answer 1

[Jan]

Assuming that m is a multiple of 24:

DataM  = reshape(Data, 24, [], 14);
Match  = (DataM(14, :, 5) >= x);
Result = reshape(DataM(:, Match, :), [], 14);

For teaching with a FOR loop:

Keep = true(1, size(Data, 1));
for k = 1:24:size(Data, 1)
  Keep(k:k+23) = (Data(k+4, 14) >= x);
end
Result = Data(Keep, :);

Answer 2

[Andrei Bobrov]

Let A - your array [m x 14]

ii = ceil((1:m)'/24);
l0 = accumarray(ii,A(:,5) >= x,[],@all);
out = A(l0(ii),:);

Answer 3

[Anushi1998]

Consider going from the end because this won't run your loop infinitely when the portion is not deleted.

Since we have to consider only segments of size 24*14 it won't affect whether we go from top to bottom or bottom to top.

 a=%array of size m * 14
 for ii=m:-24:24
   b=a(ii-23:ii,:);
   if(b(14,5)<x)
     a(ii-23:ii,:)=[];
   end
 end