Add a specific line or point in boxplots

Hi, i need help. Looked through a lot of community posts, but none helped.

I need to plot multiple boxes from which i know the lower and upper values. Futhermore within each box i need to plot a single value as point or straight line (showed in green). When i use boxplots it automatically calculates a mean value and plots it in red. I need to get rid of that and replace it with my desired green line (or as a point).

For example i saw this, where linestyle and color can be set. Can i also set the value of 'Median' ??

Thank you in advance!! :)

 load carsmall;
    boxplot(MPG)
    h = findobj(gca,'tag','Median');
    set(h,'linestyle','-.');
    set(h,'Color',[0 0 0])

Answer 1

[Voss]

Here's how you can set the value of those median lines.

In this example I'll change them from the median MPG to the mean MPG (you can make them whatever value you want):

load carsmall;
MPG = MPG+[0 10];                          % make MPG have two columns, so we get a boxplot with multiple boxes

h = boxplot(MPG);                          % make the boxplot
idx = find(strcmp(get(h,'Tag'),'Median')); % find the median lines

get(h(idx),'YData')                        % the median lines' YData is the median values

ans = 2×1 cell array
    {[24 24]}
    {[34 34]}

MPG_mean = mean(MPG,1,'omitnan')           % calculate the mean values (use whatever value you want)

MPG_mean = 1×2

23.7181 33.7181

for ii = 1:numel(idx)                      % put the median lines at the mean values
    set(h(idx(ii)),'YData',MPG_mean(ii)*[1 1]);
end

get(h(idx),'YData')                        % check that the median lines' YData is now the mean values

ans = 2×1 cell array
    {[23.7181 23.7181]}
    {[33.7181 33.7181]}

set(h(idx), ...                            % change the Color and LineWidth too
    'Color',[0 0.6 0], ...
    'LineWidth',2);

[Lorenz]

Hi @Voss,

first thank you for your quick reply, works perfectly! Do you also know if i can edit the popup windows in the figure? For my application it would be optimal to show only the maximum, the minimum and the value of the green line. Everything else is a bit disturbing since I don't use it. Thanks in andvance! :)

[Voss]

That popup is the datatip for the boxplot. To modify what it shows, you can define a custom function:

function txt = cb_update_boxplot_datatip(src,evt)

ch = reshape(get(get(src,'Parent'),'Children'),[],7);
ch = ch(end-evt.Position(1)+1,:);

tags = get(ch,'Tag');

y_min = get(ch(strcmp(tags,'Lower Adjacent Value')),'YData');
y_max = get(ch(strcmp(tags,'Upper Adjacent Value')),'YData');
y_middle = get(ch(strcmp(tags,'Median')),'YData');

txt = sprintf('Minimum: %.2f\nMaximum: %.2f\nMiddle: %.2f', ...
    y_min(1),y_max(1),y_middle(1));

end

(That same function is attached in an m-file here; you can download it.)

And then on the command line, run this command to set the UpdateFcn of the datacursormode in the current figure (assumed to be the figure that contains your boxplot) to the function you just defined:

set(datacursormode(gcf()),'UpdateFcn',@cb_update_boxplot_datatip)

Now when you have a data cursor on in that figure, it will show the custom datatip.

I labeled the green-line value as 'Middle' in the function, since it's not necessarily the median anymore, but you can change that to whatever you want it to say, or change anything else about what shows up in the datatip now.