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If I have an array and I need to find an element in the array how do I go about it?

30 vues (au cours des 30 derniers jours)
Joseph
Joseph le 28 Mai 2024 à 13:46
Commenté : William Rose le 28 Mai 2024 à 14:22
say states,
states = [1 0 0;
1 1 0
0 1 0
0 1 1
0 0 1
1 0 1
1 1 1];
C = 110;
How do I find the index of C in states and call it?
Ideally C is 2 then states(2) will give me 110 what key word can I use? or How do I go about it?

Réponse acceptée

John D'Errico
John D'Errico le 28 Mai 2024 à 14:05
Modifié(e) : John D'Errico le 28 Mai 2024 à 14:06
I think you are confusing things, not understanding there is a difference between the number 110, and the vector [1 1 0], and then of the rows of an array. This is not a question of keywords, but a question of understanding what a variable contains, and how numbers are stored.
states = [1 0 0;
1 1 0
0 1 0
0 1 1
0 0 1
1 0 1
1 1 1];
States is a 2 dimensional array. You can access the second ROW of states as:
states(2,:)
ans = 1x3
1 1 0
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Now, if you want to identify which row of states matches the vector
C = [1 1 0]
C = 1x3
1 1 0
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then you could do something like
ismember(states,C,'rows')
ans = 7x1 logical array
0 1 0 0 0 0 0
Ismemmber returns a boolean vector that tell you the set of all rows of states which match your target (in case there was more than one row.) Or you could tell find to return only the first row. So then you could do this:
find(ismember(states,C,'rows'),1,'first')
ans = 2
So find only 1 result, and make it the first row it finds, in case of multiple positive results.

Plus de réponses (2)

Torsten
Torsten le 28 Mai 2024 à 14:05
Déplacé(e) : Torsten le 28 Mai 2024 à 14:05
Compute
100*states(:,1)+10*states(:,2)+states(:,3)
and use "find" to compare with C.
  1 commentaire
Stephen23
Stephen23 le 28 Mai 2024 à 14:21
Also using matrix multiplication:
states = [1,0,0; 1,1,0; 0,1,0; 0,1,1; 0,0,1; 1,0,1; 1 1 1];
C = 110;
X = find(C==states*[100;10;1])
X = 2

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William Rose
William Rose le 28 Mai 2024 à 14:12
states = [1 0 0; 1 1 0; 0 1 0; 0 1 1; 0 0 1; 1 0 1; 1 1 1];
C = [1 1 0];
for i=1:length(states), if states(i,:)==C, idx=i; end, end
fprintf('States=C at row %d.\n',idx)
States=C at row 2.
Not elegant, but it works.
  1 commentaire
William Rose
William Rose le 28 Mai 2024 à 14:22
If there are multiple matching rows, the code above will report the last row only. In order to get all rows that match, you could do
states = [1 0 0; 1 1 0; 0 1 0; 0 1 1; 0 0 1; 1 0 1; 1 1 1; 1 1 0];
C = [1 1 0]; % states==C at rows 2 and 8
idx=[];
for i=1:length(states), if states(i,:)==C, idx=[idx,i]; end, end
disp(idx)
2 8

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