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Delete every n rows if less than x

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David du Preez
David du Preez on 2 Jun 2017
Answered: Anushi1998 on 2 Jun 2017
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

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David du Preez
David du Preez on 2 Jun 2017
I'm not really sure where to start even
Jan
Jan on 2 Jun 2017
@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
David du Preez on 2 Jun 2017
@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

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Accepted Answer

Jan
Jan on 2 Jun 2017
Edited: Jan on 2 Jun 2017
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, :);

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More Answers (2)

Andrei Bobrov
Andrei Bobrov on 2 Jun 2017
Let A - your array [m x 14]
ii = ceil((1:m)'/24);
l0 = accumarray(ii,A(:,5) >= x,[],@all);
out = A(l0(ii),:);

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Anushi1998
Anushi1998 on 2 Jun 2017
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

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