Define vector to use for colorbar

Hi,

I am plotting a bar+scatter plot where the scatter points are colored according to a separate variable. The problem I am having is that the colorbar is, for some reason that is beyond me, using the wrong values at the moment. If I just plot the scatter plot and add a colorbar, then the range of the colorbar is correct. I have been trying every solution I can come up with, but have not made any progress. Any help would be very much appreciated. Please find a working example of the code below;

figure
          subplot(2,1,1)
          a = 1;
          b = 2;
          r = (b-a).*rand(1,7) + a;
          y = r;
          rr = (b-a).*rand(1,7) + a;
          z = rr;
          x = [1:7];
          zz = rand(1,7)
          yyaxis left
          hold on
          for i = 1:7
              h=bar(i,y(i), 'FaceColor',[1 1 1], 'LineWidth',3);
              yb(i) = cat(1, h.YData);
              xb(i) = bsxfun(@plus, h(1).XData, [h.XOffset]');
              if zz(i) < 0.0300000
                  set(h,'EdgeColor','k');
              elseif zz(i) < 0.050000000
                  set(h,'EdgeColor','b');
              elseif zz(i) < 0.070000000
                  set(h,'EdgeColor','g');
              else
                  set(h,'EdgeColor','r');
              end
          end
          ylabel('hm', 'FontSize', 12, 'FontWeight', 'bold')
      for i1=1:7
              t = text(xb(i1)-0.2,yb(i1),num2str(yb(i1),'%0.3f'),...
                         'HorizontalAlignment','center',...
                         'VerticalAlignment','bottom')
                          s = t.FontSize;
                          t.FontSize = 12;
                          t.FontWeight = 'bold';
      end
          yyaxis right
          pointsize = 40;
          hh = scatter(x,z,pointsize, zz,'filled')
          cc = colormap([hsv(20)])
          c = colorbar
          c.Label.String = 'Pos';
          set(gca,'Ydir','reverse')
          ylabel('OK', 'FontSize', 12, 'FontWeight', 'bold')
          lgd = legend([h, hh], 'hm', 'OK')
      subplot(2,1,2)
      x = [1:8]
      a = 1;
      b = 2;
      r = (b-a).*rand(1,8) + a;
      y = r;
      rr = (b-a).*rand(1,8) + a;
      z = rr;
      zz = rand(1,8);
      yyaxis left
      hold on
      for i = 1:8
              h=bar(i,y(i), 'FaceColor',[1 1 1], 'LineWidth',3);
              yb(i) = cat(1, h.YData);
              xb(i) = bsxfun(@plus, h(1).XData, [h.XOffset]');
              if zz(i) < 0.0300000
                  set(h,'EdgeColor','k');
              elseif zz(i) < 0.050000000
                  set(h,'EdgeColor','b');
              elseif zz(i) < 0.070000000
                  set(h,'EdgeColor','g');
              else
                  set(h,'EdgeColor','r');
              end
      end
      for i1=1:8
              t = text(xb(i1)-0.2,yb(i1),num2str(yb(i1),'%0.3f'),...
                         'HorizontalAlignment','center',...
                         'VerticalAlignment','bottom')
                          s = t.FontSize;
                          t.FontSize = 12;
                          t.FontWeight = 'bold';
      end
      ylabel('hm', 'FontSize', 12, 'FontWeight', 'bold')
      yyaxis right
      pointsize = 40;
      hh = scatter(x,z,pointsize, zz,'filled')
      set(gca,'Ydir','reverse')
      ylabel('OK', 'FontSize', 12, 'FontWeight', 'bold')
      c = colorbar
      c.Label.String = 'Pos';
      lgd = legend([h, hh], 'hm', 'OK')
          %title(lgd,'My Legend Title')
          hold off

Thanks in anticipation.

Regards Joel

Answer 1

[Nick Counts]

Ok, I spend some time with this and I think i see what's happening. It all boils down to the way you define the CData property of your scatter plot. Here is a simple example that should illustrate how it works:

    xData = 1:10
    yData = rand(1, 10) + 1 % random number between 1 and 2

    cVect = yData;
    colormap(jet(10));

    hScat = scatter(xData, yData, 100, cVect, 'Filled')

    hcbar = colorbar
    caxis([1 2])

This sets the CData to the same value as the yData vector, and then we use caxis to determine the boundaries of the displayed color scale.

Now in your code, it looks like you are using the variable zz as your CData value in your scatter plot. You define it this way:

zz = rand(1,7)

This means it will be a 7 element vector with values between 0 and 1. When you use colormap you are creating an array of colors that your CData will be mapped to. Without specifying a caxis, I think Matlab automatically maps the bottom color to the lowest CData value, and the top color to the highest CData value.

From your code, I assume you want to map a zz value of 0 to the bottom color, and a zz value of 1 to the top color?

If so, the following simplification of your example should do the trick:

figure
  % Generate Data
      a = 1;
      b = 2;
      r = (b-a).*rand(1,7) + a;
      y = r;
      rr = (b-a).*rand(1,7) + a;
      z = rr;
      x = [1:7];
      zz = rand(1,7)

    % yyaxis left % Removed because I'm on 2014b

    % Draw rectangles    
    hold on
    for i = 1:7
        hBarGraph = bar(i,y(i), 'FaceColor',[1 1 1], 'LineWidth',3);
        yb(i) = cat(1, hBarGraph.YData);
        xb(i) = bsxfun(@plus, hBarGraph(1).XData, [hBarGraph.XOffset]');
        if zz(i) < 0.0300000
            set(hBarGraph,'EdgeColor','k');
        elseif zz(i) < 0.050000000
            set(hBarGraph,'EdgeColor','b');
        elseif zz(i) < 0.070000000
            set(hBarGraph,'EdgeColor','g');
        else
            set(hBarGraph,'EdgeColor','r');
        end
    end

    ylabel('hm', 'FontSize', 12, 'FontWeight', 'bold')

    % Text labels for rectangles
    for i1=1:7
        t = text(xb(i1)-0.2,yb(i1),num2str(yb(i1),'%0.3f'),...
                'HorizontalAlignment',  'center',...
                'VerticalAlignment',    'bottom');
                t.FontSize = 12;
                t.FontWeight = 'bold';
    end

    % yyaxis right % Removed because I'm on 2014b
  % Scatter Plot
    pointsize = 40;

    hAxes = gca;
    colormap(hsv(20))
    colorBounds = [0 1];
    caxis(colorBounds)
    colorbar

    hScatterPlot = scatter(x,z,pointsize, zz,'filled')

    set(hAxes,'Ydir','reverse')
    ylabel('OK', 'FontSize', 12, 'FontWeight', 'bold')
    lgd = legend([hBarGraph, hScatterPlot], 'hm', 'OK')

If this doesn't help, please let us know more about what color behavior you want. Good luck, and let us know how it goes! :)

[Joel]

Thank you, Nick! I really appreciate you taking the time!

Your solution is even better than what I had in mind. Initially I just wanted the colorbar to be governed by the third variable, zz, in the scatter plot. I failed with this, as the range of the colorbar was not the same as the range of the zz variable. And if I forced the colorbar to be the same range, the color of the colorbar did not match the scatter plot.

I found a way to solve this - however, your code is, a mentioned, much better! Thank you again!

I will attach my code just to show how I did it;

figure
a = 1;
b = 2;
r = (b-a).*rand(1,7) + a;
y = r;
rr = (b-a).*rand(1,7) + a;
z = rr;
x = [1:7];
zz = rand(1,7)
  colormap(jet)
  yyaxis left
  hold on
  for i = 1:length(y)
      h=bar(i,y(i), 'FaceColor',[1 1 1], 'LineWidth',3);
      yb(i) = cat(1, h.YData);
      xb(i) = bsxfun(@plus, h(1).XData, [h.XOffset]');
      if zz(i) < 0.0300000
          set(h,'EdgeColor','k');
      elseif zz(i) < 0.050000000
          set(h,'EdgeColor','k');
      elseif zz(i) < 0.070000000
          set(h,'EdgeColor','k');
      else
          set(h,'EdgeColor','k');
      end
  end

    cco = min(zz)
    cct = max(zz)
    caxis([cco cct])
    coloo = colorbar
    coloo.Label.String = 'Cbar';
    %h = bar(y, 0.2, 'FaceColor',[1 1 1], 'EdgeColor',[0 0 0],'LineWidth',2);
    %yb = cat(1, h.YData);
    %xb = bsxfun(@plus, h(1).XData, [h.XOffset]');
    for i1=1:7 % numel(yb)
        t = text(xb(i1)-0.3,yb(i1),num2str(yb(i1),'%0.3f'),...
                   'HorizontalAlignment','center',...
                   'VerticalAlignment','bottom')
                    s = t.FontSize;
                    t.FontSize = 12;
                    t.FontWeight = 'bold';
    end
    ylabel('OK', 'FontSize', 12, 'FontWeight', 'bold')
    yyaxis right
    pointsize = 80;
    hh = scatter(x,z,pointsize, zz,'filled')
    set(gca,'Ydir','reverse')
    ylabel('MM', 'FontSize', 12, 'FontWeight', 'bold')
    c = colorbar
    c.Label.String = 'Cbar';
    lgd = legend([h, hh], 'OK', 'MM')
    %title(lgd,'My Legend Title')
    hold off

Answer 2

[Nick Counts]

Joel,

I don't know about a vector, but you can set upper and lower limits. It looks like you are saving a handle to the colorbar in variable 'c'

Try:

c.Limits = [0 10]

Obviously use whatever numbers make sense for your plots :)

Good luck!

[Nick Counts]

Also, checkout

doc colormap

There are good examples there that may help you with defining your own vector

[Joel]

Thank you! This seemed really promising, however the problem I am facing when using

c.Limits = [0 1]

is that the colorbar then does not match the color of the scatter plot anymore.

Any idea why this could be? It seems the colorbar does not use the vector that is used to color the scatter plot as input.

Regards Joel

[Nick Counts]

I just realized that I wasn't really answering your question!

caxis([0.0826    0.7505])

Try this - and change the numbers around. It maps the bottom color to the first value and the top color to the second number. From the documentation:

caxis([cmin cmax]) sets the color limits to specified minimum and
maximum values. Data values less than cmin or greater than max map
to cmin and cmax, respectively. Values between cmin and max
linearly map to the current colormap.

That was more confusing than I wanted, but hopefully it makes sense

[Joel]

Thank you, Nick!

Whilst I've still not solved the question, I've narrowed down the source of the error.

If I use

caxis

to print out the values of caxis they look just like they should. The lower and upper limits are what they should be.

However, the colorbar is still not synchronized with caxis, for some reason. The original range of the colorbar i between 1 and 2.

If I change this using the following code,

c = colorbar
cc = caxis
c.Limits = [cc(1) cc(2)]

The resulting colorbar is simply a capped version of the previous colorbar. That is, the full color-range is not present - the color-range is what c.Limits would have been before. For example, if my original colorbar is between red and blue, the new colorbar is just red. It is tricky to explain, but I hope I make some sense.

Regards Joel