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

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?

Answer 1

[John D'Errico]

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.

[Joseph]

Thanks for the clarification, It works

Answer 2

[Torsten]

Compute

100*states(:,1)+10*states(:,2)+states(:,3)

and use "find" to compare with C.

[Stephen23]

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

Answer 3

[William Rose]

@Joseph,

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.

[William Rose]

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