How to a find the frequency of a point or values?

If I have a Nx2 vector (in this case, N=20): A =

     0     1
     0     1
     1     0
     0    -1
     0    -1
    -1     0
    -1     0
     0     1
     0     1
     1     0
     0    -1
     0    -1
    -1     0
    -1     0
     0     1
    -1     0
     1     0
     0    -1
     0    -1
    -1     0

I want to know how many times each unique point (-1,0), (1,0), (0,1), and (0, -1) appears in this vector. For example, the point (-1,0) occurs 6 times. Is there a fast, simple way to do this? Using the find function or a for loop were too cumbersome I thought, but I couldn't find a simple function that would help with this. Is anyone aware of a function, or a simple method to accomplish this? Thanks

Answer 1

[Mahdiyar]

Hi

you can download the matlab function named findsubmat from the following link. Then use it for each pair. For example:

B1 = findsubmat(A, [-1 0]);
B2 = findsubmat(A, [1 0]);
B3 = findsubmat(A, [0 1]);
B4 = findsubmat(A, [0 -1]);

http://it.mathworks.com/matlabcentral/fileexchange/23998-findsubmat

Regards,

[John Alperto]

This is pretty interesting. I was hoping for something a little more simple (i.e., something that wouldn't require a separate function, or that many lines of code), but I certainly wouldn't be opposed to using this if it ends up being my only option. Thanks for pointing it out.

[Mahdiyar]

Please follow the code below:

A =[ 0     1
     0     1
     1     0
     0    -1
     0    -1
    -1     0
    -1     0
     0     1
     0     1
     1     0
     0    -1
     0    -1
    -1     0
    -1     0
     0     1
    -1     0
     1     0
     0    -1
     0    -1
    -1     0];

D1 = 0; D2 = 0; D3 = 0; D4 =0;
for i=1:size(A,1)
  B = A(i,:);

    C = B - [-1 0];
    NZ = length(find(C==0));
    if NZ == 2
        D1 = D1 +1;
    end

    C = B - [1 0];
    NZ = length(find(C==0));
    if NZ == 2
        D2 = D2 +1;
    end

    C = B - [0 1];
    NZ = length(find(C==0));
    if NZ == 2
        D3 = D3 +1;
    end

    C = B - [0 -1];
    NZ = length(find(C==0));
    if NZ == 2
        D4 = D4 +1;
    end

end

[D1 D2 D3 D4]

[John Alperto]

Thanks.

Answer 2

[Star Strider]

This works:

A = [0     1
     0     1
     1     0
     0    -1
     0    -1
    -1     0
    -1     0
     0     1
     0     1
     1     0
     0    -1
     0    -1
    -1     0
    -1     0
     0     1
    -1     0
     1     0
     0    -1
     0    -1
    -1     0];

[Au,~,ic] = unique(A,'rows');
k = accumarray(ic,1);
fprintf('\n\tPoints\tFrequency\n')
fprintf('\t%2d %2d\t\t%2d\n', [Au k]')

and produces:

  Points  Frequency
  -1  0        6
   0 -1       6
   0  1       5
   1  0       3