Asked by Andy
on 18 Feb 2013

I want to be able to plot my points in a scatter plot and if the points are within the co ordinates of two circles they will be plotted in different colours. At the moment i can plot my points within the limits i need.

x = randi([-35,165],[2000,1]); x = x'; y = randi([-20,80],[2000,1]); y = y'; plot(x,y,'kx','LineWidth',2,'MarkerSize',10)

I can also plot points with different colours within two circles.

num1 = 2000; radius = 30;

theta = rand(1,num1)*(2*pi); r = sqrt(rand(1,num1))*radius; xCor = r.*cos(theta); yCor = r.*sin(theta);

plot(xCor,yCor,'rx','LineWidth',2,'MarkerSize',10)

subplot(1,1,1) hold on; num = 1000; rad = 10; theta = rand(1,num)*(2*pi); r = sqrt(rand(1,num))*rad; xCor2 = r.*cos(theta); yCor2 = r.*sin(theta); plot(xCor2,yCor2,'gx','LineWidth',2,'MarkerSize',10)

What i cant seem to work out is how do i use the original points in my first section of code and then change the colour points which are within the limits of a circle (with a given centre point)? I am aiming not to use loops as well.

Thanks You

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Answer by bym
on 19 Feb 2013

Maybe this will help as an example:

clc;clear x = rand(1000,1); y = rand(1000,1); yg = y; yg(hypot(x-.5,y-.5)<.25)=NaN; yb = y; yb(hypot(x-.5,y-.5)>=.25)=NaN; plot(x,[yg yb],'.') axis square

Answer by Image Analyst
on 19 Feb 2013

And a slight variation where the points *continuously* vary color from the center of the circle:

x = rand(1000,1); y = rand(1000,1); distances = ((x-.5).^2 + (y-0.5).^2).^0.5; % Normalize - divide my sqrt(maxX^2 + maxY^2) distances = distances / sqrt(.5^2 + .5^2); [sortedDistances sortIndexes] = sort(distances); % Arrange the data so that points close to the center % use the blue end of the colormap, and points % close to the edge use the red end of the colormap. xs = x(sortIndexes); ys = y(sortIndexes); cmap = jet(length(x)); % Make 1000 colors. scatter(xs, ys, 10, cmap, 'filled') grid on; title('Points where color depends on distance from center', ... 'FontSize', 30); % Enlarge figure to full screen. set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Give a name to the title bar. set(gcf,'name','Demo by ImageAnalyst','numbertitle','off')

Answer by Walter Roberson
on 19 Feb 2013

Use scatter() instead of plot(). The C (color) parameter of scatter() can be an array of RGB rows, one row per point.

Answer by Andy
on 19 Feb 2013

Thank you for the replies. I managed to work it out with a combination in the end. In the end i used a for loop, going through my generated numbers. I then checked the distance of the co ordinates away from the centre point of my circle and plotted them with the right colour accordingly.

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