omit rows of matrix based on a condition

Hello

My matrix B is :

[0.25 0 0;

0.5 -4.91 -4.9;

0.75 -4.94 -4.96;

1 -4.985 -5;

1.25 -5 -5;

1.5 -5 -5;

1.75 -5 -5]

How to write a code to omit all the rows (except from first row and fifth row 1.25,-5,-5) where column 2 and three are equal. I mean keep the first and fifth row where column 2 and 3 are equal but omit other rows with the same situation.

Answer 1

[David Hill]

Seems like there are more than just two rows.

B=[0.25	0	0;
0.5	-4.91  -4.9;
0.75	-4.94  -4.96;
1	-4.985	-5;
1.25	-5	-5;
1.5	-5	-5;
1.75	-5	-5];
[~,idx]=unique(B(:,2),'stable');
C=B(idx,:);
C(C(:,2)~=C(:,3),:)=[];
C

C = 2×3

0.2500 0 0 1.2500 -5.0000 -5.0000

[Pooneh Shah Malekpoor]

Thanks, Then how to get [0.25 0 0;

0.5 -4.91 -4.9;

0.75 -4.94 -4.96;

1 -4.985 -5;

1.25 -5 -5]???

[David Hill]

B=[0.25	0	0;
0.5	-4.91  -4.9;
0.75	-4.94  -4.96;
1	-4.985	-5;
1.25	-5	-5;
1.5	-5	-5;
1.75	-5	-5];
[~,idx]=unique(B(:,2),'stable');
C=B(idx,:)

C = 5×3

0.2500 0 0 0.5000 -4.9100 -4.9000 0.7500 -4.9400 -4.9600 1.0000 -4.9850 -5.0000 1.2500 -5.0000 -5.0000

Answer 2

[Torsten]

B = [0.25	0	0;
    0.5	-4.91  -4.9;
    0.75	-4.94  -4.96;
    1	-4.985	-5;
    1.25	-5	-5;
    1.5	-5	-5;
    1.75	-5	-5];
B = B(union(find(B(:,2)~=B(:,3)),[1 5]),:)

B = 5×3

0.2500 0 0 0.5000 -4.9100 -4.9000 0.7500 -4.9400 -4.9600 1.0000 -4.9850 -5.0000 1.2500 -5.0000 -5.0000

Answer 3

[Ghazwan]

%If you already know that you need to omit the first and last row only
A=A(2:end-1,:);
%If you do not know which rows have the condition
for ii=1:length(A(:,1))
    if A(ii,2)==A(ii,3)  %Your condition
        A(ii,:)=[];  %omitting the row that meets the condition
    end
end

[Pooneh Shah Malekpoor]

Thanks but it keeps the last row while I want it to keep the first row with equal arrays in column 2 and 3 (I mean I want a for loop which keep the fifth row). How?