Problem with individual colour display in Legend for scatter plot (2014b)

I am plotting a scatter plot within a loop and then assigning a legend outside the loop for all the data (15 sets). In previous versions of Matlab the legend would match the colours used in the scatter plot to differentiate between the 15 datasets. In the latest release the legend only shows one colour for each dataset (despite the plot showing different ones).

Anyone know a reason/workaround?

code...

C=[1:1:15]; subplot(212); hold on

for i=1:15;

    if ~isempty(Pro_PT(1,i).BurstTime);
        B=repmat(C(i),length(Pro_PT(1,i).Stats(:,2)),1);
        scatter(Pro_PT(1,i).Stats(:,2),Pro_PT(1,i).Stats(:,3),15,B,'filled','o');
        leg{i}=['PT ',num2str(i)];L{i}=i;
    else
        leg{i}=num2str(NaN);L{i}=NaN;
    end

end a=~isnan(cell2mat(L)); l=leg(a); legend(l,'Location', 'NorthWest','FontSize',6);

Answer 1

[Alexander Mueller]

Here is the workaround again with the code formatting cleaned up.

C=[1:1:15]; subplot(212); hold on
cm = parula(15);
colormap(cm)
for i=1:15;
  if ~isempty(Pro_PT(1,i).BurstTime);
      B=repmat(cm(i),length(Pro_PT(1,i).Stats(:,2)),1);
      scatter(Pro_PT(1,i).Stats(:,2),Pro_PT(1,i).Stats(:,3),15,B,'filled','o');
      leg{i}=['PT ',num2str(i)];L{i}=i;
  else
      leg{i}=num2str(NaN);L{i}=NaN;
  end  
end

[Tim]

Hi Alexander, Thanks for this but i still get all the same colours for the data in the legend- no change?

[Benjamin Kraus]

Tim,

There was a typo in Alexander's code.

B=repmat(cm(i),length(Pro_PT(1,i).Stats(:,2)),1);

should be:

B=repmat(cm(i,:),length(Pro_PT(1,i).Stats(:,2)),1);

(note "cm(i,:)" instead of "cm(i)").

It would also work to just use this:

B=cm(i,:);

Both approaches are specifying the color using an RGB value. The first provides one RGB value for each point in the scatter plot, but all the RGB values are the same. Because all the points in each call to 'scatter' are the same color, the second approach specifies just one color for the each set of points (instead of each individual point).

- Ben

[Tim]

Hi Ben, Thanks for the correction and I can confirm this gives the right result. Frustrating and odd that the latest Matlab version has a bug/does not work like previous versions, but thank you for the workaround.

Answer 2

[Alexander Mueller]

Tim Since you know the number of unique colors you'll need, 15, you can generate an explicit list of RGB colors and pass them into scatter as an Mx3 matrix.

C=[1:1:15]; subplot(212); hold on cm = parula(15); colormap(cm) for i=1:15;

    if ~isempty(Pro_PT(1,i).BurstTime);
        B=repmat(cm(i),length(Pro_PT(1,i).Stats(:,2)),1);
        scatter(Pro_PT(1,i).Stats(:,2),Pro_PT(1,i).Stats(:,3),15,B,'filled','o');
        leg{i}=['PT ',num2str(i)];L{i}=i;
    else
        leg{i}=num2str(NaN);L{i}=NaN;
    end  
end