How to keep rows whose values follow a certain sequence?

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Lu Da Silva
Lu Da Silva 2022-2-3
评论： Stephen23 2022-2-3
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 个评论
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Stephen23
Stephen23 2022-2-3
编辑：Stephen23 2022-2-3
"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 2022-2-3
编辑：Lu Da Silva 2022-2-3
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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采纳的回答

Stephen23
Stephen23 2022-2-3
编辑：Stephen23 2022-2-3
Ran in:
Here is an old MATLAB trick that you can use, which still works today:
https://blogs.mathworks.com/loren/2008/09/08/finding-patterns-in-arrays
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

更多回答（1 个）

David Hill
David Hill 2022-2-3
s=strfind(num2str(yourMatrix(:,1))','123');
newMatrix=[];
for k=1:length(s)
newMatrix=[newMatrix;yourMatrix(s(k):s(k)+2,:)];
end
  2 个评论
Lu Da Silva
Lu Da Silva 2022-2-3
I tried your suggestion but I get an error:
Error using strfind
First argument must be text
David Hill
David Hill 2022-2-3
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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