How to count the each pair of sequence apeared

Hi, I have below array (of three columns).I want to count how many times B appeared after A (or B) or A appeared after B (or A). Here I only shown A&B combination, but actually I have A~Z combinations(26by26 matrix).Kindly help me, many thanks in advance.

A   
B     
B   
A   
A   
B

I

Answer 1

[Image Analyst]

Try this:

% Create sample data.
m= ['A','B','C','A','B';'Q','A','B','E','R';'A','B','A','B','B']
[rows, columns] = size(m);
for row = 1 : rows
  % Find the locations and print them out.
  loc = strfind(m(row,:), 'AB');
  fprintf('\nFor row %d, AB occurs %d times, at these locations: ', ...
    row, length(loc));
  fprintf('%d ', loc);
end
fprintf('\n'); % Add a line feed after all the numbers.

In the command window:

m =
ABCAB
QABER
ABABB

For row 1, AB occurs 2 times, at these locations: 1 4 
For row 2, AB occurs 1 times, at these locations: 2 
For row 3, AB occurs 2 times, at these locations: 1 3

[EDIT]

If you have the Image Processing Toolbox, you can do this for all letters in a single line of code if you use the function graycomatrix().

[Mekala balaji]

Sir,

Mine is column vector, and I want to know how many times A appeared after A or B, and B appeared after A or B. Here I only give A, B. But I have all A~Z combination (26by26 matrix). Its like permutations and combinations. Please help. For instance in this example, B appeared three times at row2 after A, at row3 after B, and at row6 B after A. Like this count I want. I attached the example. Here. AA means A runs after A, AB means B runs after A, BB means B runs after B, and BA means A runs after B. Thanks in advance.

[Image Analyst]

Your data looks like this:

1  A
2  B
3  B
4  A
5  A
6  B

I don't understand this: "B appeared three times at row2 after A". In row 2 there is only a B. There is no B following an A - not even once, much less 3 times. Are you seeing something in row 2 that I'm not seeing? Even if you look at all rows simultaneously, B occurs in a row immediately after A only twice, not 3 times. So I don't know what you're saying. Please clarify.

[Mekala balaji]

Sir,

First columns in my matrix is row numbers. B appeared at row2(after A),row3(after B), and row6(afterA). Same as A appeared at row4 (after B),at row 5(after A). A also appeared at row but nothing before that, that why I did not counted.

B appeared after A at row2 means, B is at row2 and at row1 is A, I meant this is B appeared after A.

[Image Analyst]

So you are looking at all the rows in the column. Okay, but your explanation also says that B occurs after A only twice - when there was a B in rows 2 and 6 - so why did you say that "B appeared three times" after A?

Do you really mean that you want to count the total number of B's in a column but only once A has occurred in a row? Like if the first A is in row 42, you want the count of the number of B's in rows 43 until the end?

[Mekala balaji]

Sir, I don't mind B appeared after A or after B itself (like at row3). I just want to count how it appeared (that is after A or after B itself) but how many time B appeared after A, and B appeared after B it self. Same as for A. That's why I want to count as below matrix: The combination matrix is as below (as we knew):

AA  AB
BA  BB

As I said before, AA means A after A, AB means B after A, BA means A after B, and BB means B after B. I want to check and count how many times we have these sequences. My resultant count matrix is as below:

Resultant matrix(of count)

1  2
1  1

AA count =1, because A appeared after A only once at row5. AB count is 2, it means B appeared after A twice at row2 and row6. BA count is 1 because A appeared after B only once at row4. Finally, BB count is 1, since B appeared after B only once at row3.

[Image Analyst]

If I understood you correctly, this should do it:

% Create sample data.
rows = 200;
columns = 2;
% Make array, of 2 columns, with random letters.
m = char(randi([1,26], rows, columns) + 'A' - 1);
[rows, columns] = size(m);
counts = zeros(26, 26);
for col = 1 : columns  % For columns 1 and 2...
  % Extract only this row.
  thisColumn = m(:, col); 
  for c1 = 1 : 26  % for every character
    thisChar = c1 + 'A' - 1;
    % Find first instance of this letter in the column
    firstIndex = strfind(thisColumn', thisChar);
    if isempty(firstIndex)
      % Character is not in this row. 
      fprintf('%c not found in column %d\n', thisChar, col);
      % Skip to the next character
      continue;
    end
    % Now extract the column from this point down,
    % Because we only want to consider how many times
    % a letter occured AFTER this index, not before.
    subColumn = thisColumn(firstIndex:end);
    for c2 = 1 : 26  % for every character
      otherChar = c2 + 'A' - 1;
      % Get a logical vector of where otherChar occurs
      locations = strfind(subColumn', otherChar);
      if ~isempty(locations)
        % If the other character appears
        % count the number of times and assign it.
        numTimes = length(locations);
        counts(c1, c2) = numTimes;
        fprintf('%c appears %d times after %c in column %d\n', otherChar, numTimes, thisChar, col);
      end
    end
  end
end
counts % Echo to command window