adding values to vector

Hello, I have this vector that is constantly changing values for instance the below output might look something like

 v =

     4    15
     3    15
     3    16
     3    15
     2    15

And this will continue to happen till the step size is reached. I do not want any value in the array to repeat ! How do I do this? So 3 15 was repeated twice, I want to force the program to move to a different coordinate versus repeating values. See code below

if true
  %Random walk in 2D, periodic boundaries
%The script simulates a random walk with periodic boundary conditions. The
xmax = 20; %grid size
ymax = 20; %grid size
nsteps = 400; %number of steps in the simulation
x = round(5);
y = round(15);
plot(x,y,'bo')
ht = title('Steps taken = 0');
h = [];
axis([0.8 xmax+0.2 0.8 ymax+0.2])
hold on
v=[]
for i = 1:nsteps
 d = randi(4); %direction (north(1), west(2), south(3), east(4))
 dx = 0;
 dy = 0;
 switch d
    case 1
       dy = 1;
    case 2
       dx = -1;
    case 3
       dy = -1;
    case 4
       dx = 1;
 end
 nx = x + dx;
 ny = y + dy;

 v(end+1,:)=[nx,ny] %Recording all the steps take

   %Now apply periodic boundary conditions
   if nx<1
      x = x + xmax;
      nx = nx + xmax;
   elseif nx>xmax;
      x = x - xmax;
      nx = nx - xmax;
   end
   if ny<1
      y = y + ymax;
      ny = ny + ymax;
   elseif ny>ymax;
      y = y - ymax;
      ny = ny - ymax;
   end
   %Draw a line from the current position to the next position
   if ~isempty(h)
       set(h,'MarkerEdgeColor','b')
   end
   line([x nx],[y ny])
   h = plot(nx,ny,'r*');
   set(ht,'String',['Steps taken = ' num2str(i)])
   x = nx;
   y = ny;
   pause(0.1) %the pause that refreshes
end
hold off
  end

Answer 1

[Azzi Abdelmalek]

unique(v,'rows')

%Or maybe you want something like this:

v=[4    15; 3    15]
c=[3 15]
if ismember(c,v,'rows')
   %skip
else
   %do
end

[Jessica Benidict]

how do i say if a row,column == another row,column in the same matrix?

[Azzi Abdelmalek]

Your comment is not clear

[Image Analyst]

Maybe

if matrix1(row, column) == matrix2(row, column)

??? But like Azzi said, it's not clear what you want. If the matrices are floating point numbers, be sure to read the FAQ.