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How to keep rows whose values follow a certain sequence?

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Lu Da Silva
Lu Da Silva el 3 de Feb. de 2022
Comentada: Stephen23 el 3 de Feb. de 2022
I have a matrix composed of two columns A and B, I need to only keep the rows which contain the sequence 90-180-270:
A B A B
-------- ----------
90 1 90 1
180 9 180 9
270 2 270 2
90 0 -> 90 0
270 3 180 4
90 0 270 6
180 4
270 6
How can I implement this into a Matlab code?
  5 comentarios
Stephen23
Stephen23 el 3 de Feb. de 2022
Editada: Stephen23 el 3 de Feb. de 2022
"It only includes three possible numbers: 180, 270 and 90. (I wrote 1 2 3 for simplicity reasons)."
It is more complex and slower. Because solutions that work with 1-2-3 might not work with other values. But because you gave us incorrect information we all spend our time developing solutions that might not suit your needs at all.
You should tell us the exact values and the exact order.
Lu Da Silva
Lu Da Silva el 3 de Feb. de 2022
Editada: Lu Da Silva el 3 de Feb. de 2022
Yes, the actual sequence is 90, 180, 270. But that shouldn't matter, the code should work for any given sequence.

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Stephen23
Stephen23 el 3 de Feb. de 2022
Editada: Stephen23 el 3 de Feb. de 2022
Here is an old MATLAB trick that you can use, which still works today:
Where M is your matrix and S is the desired sequence:
S = [90,180,270]; % the required sequence
M = [90,1;180,9;270,2;90,0;270,3;90,0;180,4;270,6]
M = 8×2
90 1 180 9 270 2 90 0 270 3 90 0 180 4 270 6
X = strfind(M(:,1).',S);
Y = X-1+(1:numel(S)).';
Z = M(Y,:)
Z = 6×2
90 1 180 9 270 2 90 0 180 4 270 6
  3 comentarios
Stephen23
Stephen23 el 3 de Feb. de 2022
@David Hill: just two steps: STRFIND and some simple indexing :)

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Más respuestas (1)

David Hill
David Hill el 3 de Feb. de 2022
s=strfind(num2str(yourMatrix(:,1))','123');
newMatrix=[];
for k=1:length(s)
newMatrix=[newMatrix;yourMatrix(s(k):s(k)+2,:)];
end
  2 comentarios
Lu Da Silva
Lu Da Silva el 3 de Feb. de 2022
I tried your suggestion but I get an error:
Error using strfind
First argument must be text
David Hill
David Hill el 3 de Feb. de 2022
This should work.
r=yourMatrix(:,1);
r(r==90)=1;r(r==180)=2;r(r==270)=3;%change based on sequence desired
f=strfind(num2str(r)','123');
newMatrix=[];
for k=1:length(f)
newMatrix=[newMatrix;yourMatrix(f(k):f(k)+2,:)];
end

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