How to keep rows whose values follow a certain sequence?
显示 更早的评论
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
Stephen23
2022-2-3
What are the possible values in column A ? Can it also include 4, 5, 9, 123, or does it include only 1, 2, & 3 ?
Lu Da Silva
2022-2-3
编辑：Lu Da Silva
2022-2-3
David Hill
2022-2-3
Do you want 90,180,270 sequence?
"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
2022-2-3
编辑：Lu Da Silva
2022-2-3
采纳的回答
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]
X = strfind(M(:,1).',S);
Y = X-1+(1:numel(S)).';
Z = M(Y,:)
3 个评论
Lu Da Silva
2022-2-3
David Hill
2022-2-3
Very tricky
Stephen23
2022-2-3
@David Hill: just two steps: STRFIND and some simple indexing :)
更多回答（1 个）
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
2022-2-3
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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