How to find the position of a given vector A in a matrix M when the size of vector A is smaller than the columns of that matrix?

I trying to find the (row) postion of A = [15 2] in a matrix M.

M = [46 58 50

46 41 49

15 2 1

16 2 15

21 16 15

14 16 20

16 23 20]

The solution is pos = [3 4] as the vector A are in 3 and 4 rows of M.

Answer 1

[Voss]

Here's one way, assuming you want to match A or its reverse and that the elements have to be contiguous:

M = [46	58	50
46	41	49
15	2	1
16	2	15
21	16	15
14	16	20
16	23	20];

A = [15 2];

pos = [];
for ii = 1:size(M,1)
    if ~isempty(strfind(M(ii,:),A)) ... % check if A is in row ii of M
            || ~isempty(strfind(M(ii,:),A(end:-1:1))) % or the reverse of A is in row ii of M
        pos(end+1) = ii;
    end
end

disp(pos)

     3     4

[GANESH R]

This is not working for the case when M = [14 5 4

16 4 3

14 4 16

33 29 26

35 38 40

2 16 3]

and

A = [16 3].

[GANESH R]

I found the answer.

M =

14 5 4

16 4 3

14 4 16

33 29 26

35 38 40

2 16 3

>> A

A =

16 3

>> pos = find(sum(ismember(M,A),2)==2)

pos =

2

6

[Voss]

Ah, ok. I wasn't sure if elements from A that are separated in a row of M should be counted as a match, which is why I said "that the elements have to be contiguous" in my answer.

Your solution will work if the elements in a given row of M are distinct, but consider the following situation, where I've modified row 3 of M:

M = [14	5	4
16	4	3
16	4	16
33	29	26
35	38	40
2	16	3]

M = 6×3

14 5 4 16 4 3 16 4 16 33 29 26 35 38 40 2 16 3

A = [16 3]

A = 1×2

16 3

pos = find(sum(ismember(M,A),2)==2)

pos = 3×1

2 3 6

Now row 3 is counted because it has two 16's. To handle that situation correctly, you can do this instead:

pos = [];
for ii = 1:size(M,1)
    if all(ismember(A,M(ii,:)))
        pos(end+1) = ii;
    end
end
disp(pos);

     2     6

This counts a row of M if all elements of A are found in that row. It doesn't take into account the order of the elements of A in the row of M, as my initial answer did.