Removing rows in a matrix

Hello,

I have this matrix, called A matrix. I am attaching the file with the question. Also the picture of some of its data values

I need to remove some of its rows in a loop. I want to keep rows 1,2 then remove 3,4,5,6, keep 7,8,then remove 9,10,11,12, keep 13,14.. like this it goes on.keep 2 remove 4 rows.

Does anyone know?

Answer 1

[Ameer Hamza]

Try this

n = size(Identify_3);
idx = (mod((1:n)-1, 6)+1) <= 2;
Identify_3 = Identify_3(idx, :);

[Chris Dan]

Thanks :)

[Chris Dan]

Ameer Hamza

Hi,

Can you also tell about this matrix:

How can i edit your code to keep the rows 1.48,96,144,192 and so on, basically after the first row, we take 48th row and then double 49+48=96 and so on...

Also if I want to change your code for the original matrix, what should I change?

[Ameer Hamza]

You can do it like this

D = C([1 48:48:end], :)

Answer 2

[Bjorn Gustavsson]

If you can determine/calculate all rows you want to remove at once it is best to do the re-sizing of the array at once, instead of row-by-row (if I've understood this right, the reallocation-operation is the main argument to not automatically and incrementally grow arrays, ought to be similar for shrinking.):

idx2remove = [];
for i1 = 1:size(A,1)
    if some_conds(A(i1,:))
        idx2remove = [idx2remove,i1];
    end
end
A(idx2remove,:) = [];

Ah, if you have to remove rows [3,4,5,6]+6*n then something like this should work:

idx2remove = 1:size(A,1);
idx2remove = reshape(idx2remove,6,[]);
idx2remove = idx2remove(3:end,:);
A(idx2remove(:),:) = [];

If this doesn't work out because your A doesn't have a multiple of 6 rows, then you'll have to modify the creation of the remove-array a bit. You could also go for creating an array with row-indices to keep and do:

A = A(idx2keep,:);

HTH

[Chris Dan]

Thanks :)

Answer 3

[KSSV]

Let A be your data. It seems every four rows have real value of complex number very less. We can use keep these rows.

idx = real(abs(A(:,1)))<=10^-10 ;  % this will give indices of what you want to keep
iwant = A(idx,:)

[Chris Dan]

Thanks :)