choose two coordinates

hi there, i have a set of xy coordinates show in command window.So, I want to pick the coordinate where, there are the most many number repeated in y. here i attach the illustration for reference. see the attached for more information.

http://i1259.photobucket.com/albums/ii548/msaiful89/nombor.png

help me please.. thanks

Answer 1

[Matt Tearle]

idx = (y == mode(y));
x(idx)
y(idx)

or, if x and y are columns of a matrix

idx = (xy(:,2) == mode(xy(:,2)));
xy(idx,:)

EDIT TO ADD:

Note sure if I'm correctly interpreting your follow-up question, but try this (try a few times, because random numbers sometimes do strange things):

xy = randi(10,12,2);  % Make some fake data

% Find the coordinates with the most equal y values
idx = (xy(:,2)==mode(xy(:,2)));

mostycoords = xy(idx,:);

% Take first and last coordinates  
firstlast = mostycoords([1,end],:);

% Plot results
plot(xy(:,1),xy(:,2),'o',firstlast(:,1),firstlast(:,2))
axis([0,12,0,12])

[mohd]

thanks a lot sir..:-).you are very good response and understanding.:-). the code really i need. question again.. how to plot using that coordinates. i want to draw straight line using that coordinate on my image.

Answer 2

[Image Analyst]

Try this:

% Generate some sample data,
xy = [0 3; 1 2;3 4; 3 2; 2 5; 7 2; 3 9]
modeRowIndexes = xy(:,2) == mode(xy(:,2))
% Now we know the rows that have the mode in the second column.
% So now we can find the first and last row where they occur.
firstRow = find(modeRowIndexes, 1, 'first')
lastRow = find(modeRowIndexes, 1, 'last')
% Get the first occurrence (coordinate) into a 1 by 2 array.
firstCoordinate = [xy(firstRow, 1), xy(firstRow, 2)]
% Get the second occurrence (coordinate) into a 1 by 2 array.
lastCoordinate = [xy(lastRow, 1), xy(lastRow, 2)]

In the command window you'll see the explanation:

xy =
     0     3
     1     2
     3     4
     3     2
     2     5
     7     2
     3     9
modeRowIndexes =
     0
     1
     0
     1
     0
     1
     0
firstRow =
     2
lastRow =
     6
firstCoordinate =
     1     2
lastCoordinate =
     7     2

[mohd]

wow.. it really make me happy and has fun in matlab. thanks a lot sir..;-). i'm so worry if everyone can not understand what i mean. but it is easy to get understand my question. again thanks.