randomly selecting and deleting rows from a matrix

b = X; %X is a 600 by 40 matrix

xnew = b(randperm(427),:);

i want to determine the 173 rows in b that were not selected i could also delete the selected 427 rows from b to obtain the remaining unselected rows can anyone help me do this?

your help is much appreciated

Answer 1

[James Tursa]

Your code is likely not doing what you think it is doing. The randperm(427) call gives you a permutation of the numbers 1,2,...,427. So ALL of the rows from 1-427 are selected and the rows not selected are always 428-600. From your description, it sounds like what you really wanted was to randomly select 427 out of 600. I.e., is this what you really want?

k = randperm(600,427);  % <-- 427 random integers from the set 1-600 (no replacement)
xnew = b(k,:);   % <-- select the random rows
m = ~ismember(1:600,k);  % <-- get logical indexes of other rows
xother = b(m,:);  % <-- the other rows

Another way to get the other rows per your suggestion:

xother = b;
xother(k,:) = [];

[fafz1203]

Thank you much!

Answer 2

[Yushuo]

I just used if the code line number divide by 2 reminder is 0 then delete it

A=[0.5666    0.3169 ;   0.5181    0.3317  ;  0.6645    0.0650 ;   0.0188    0.5120 ;   0.8007    0.4257 ];
disp (A);
for oooo=1:size(A,1)
    if rem(oooo , 2)==0
    A(oooo,:)=[];
      
    end
end

disp (A);