omit rows of matrix based on a condition

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Pooneh Shah Malekpoor
评论： David Hill 2022-10-15
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.

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采纳的回答

David Hill
David Hill 2022-10-15
编辑：David Hill 2022-10-15
Ran in:
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
  2 个评论
Pooneh Shah Malekpoor
Pooneh Shah Malekpoor 2022-10-15
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
David Hill 2022-10-15
Ran in:
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

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更多回答（2 个）

Torsten
Torsten 2022-10-15
Ran in:
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
Ghazwan
Ghazwan 2022-10-15
%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
  1 个评论
Pooneh Shah Malekpoor
Pooneh Shah Malekpoor 2022-10-15
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?

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