Removing rows with identical values in four columns.

Hello. I have a large matrix with dimensions of 300123 x 8.

As a note, I would like to say that in the matrix, column 1 to column 4 are time data (year, month, day, hour), and column 5 to column 8 are meteorological data measurements.

I want to delete all rows which have the same elements in column 1, column 2, column 3 and column 4.

For instance: a = [2009,10,9,5,0,0,0,0; 2009,10,2,5,3,8,7,7; 2009,10,9,5,2,1,9,1] => [2009,10,2,5,3,8,7,7]

In this example, column 1 to column 4 has repeated values in row 1 and row 3 (2009,10,9,5), and both rows are completely removed.

I want to implement this kind of solution to my whole matrix with dimensions of 300123 x 8.

Thanks in advance.

Answer 1

[Azzi Abdelmalek]

a = [2009,10,9,5,0,0,0,0
  2009,10,2,5,3,8,7,7
  2009,10,9,5,2,1,9,1
  2004,10,9,5,2,1,9,1
  2004,10,9,5,2,1,9,1
  2004,10,9,5,2,1,9,1
  2004,10,9,5,2,1,9,1
  2024,10,9,5,2,1,9,1]
[ii,jj,kk]=unique(a(:,1:4),'rows','stable');
uu=accumarray(kk,1);
w=logical(zeros(numel(kk),1))
for k=1:numel(uu)
  if uu(k)>1
      w=w | (kk==k);
  end
end
a(w,:)=[]

[Miguel L]

It works.

Thanks Azzi.