MATLAB: Display mean of data on a boxchart

MATLABplot

I need to show the mean of each box plot on the figure. here is the code to generate my box plot:

x = 1:numel(data);
colors = rand(numel(data), 3);
figure();
ax = axes();
hold(ax);
for i=1:numel(data)
    boxchart(x(i)*ones(size(data{i})), data{i},'MarkerStyle','none', ...
        'BoxFaceColor', colors(i,:), ...
        'LineWidth', 0.5, ...
        'WhiskerLineStyle', '-')
end
set(gca,'xtick',[])

When I had just one boxplot I simply used this line:

hold on
plot(mean(x), '*')

But here when I use it in the code:

x = 1:numel(data);
colors = rand(numel(data), 3);
figure();
ax = axes();
hold(ax);
for i=1:numel(data)
    boxchart(x(i)*ones(size(data{i})), data{i},'MarkerStyle','none', ...
        'BoxFaceColor', colors(i,:), ...
        'LineWidth', 0.5, ...
        'WhiskerLineStyle', '-')
    plot(mean(data{i}), '*') %%%%%%%%%%<<<<<<<<<<<<< HERE
end
set(gca,'xtick',[])

It shows all mean values on the first boxplot only, meanwhile I need to have one * as a mean value for each boxplot.

Best Regards

Best Answer

"??? There's a boxplot, no info on boxchart"

Well, bless their little pea-pickin' hearts but TMW has done it again...introduced yet another duplicated function with different name and slightly different syntax/characteristics. I wish they would quit doing that and do something really new and different like introduce a hatching pattern or something instead...

Anyways my rant aside, looks like you're going at this the hard way. Reading between the lines, it looks like you have a cell array of numel() elements and you're iterating over it to plot each cell separately.

Instead

figure;
y=cellmat(data);                            % convert the cell array to matrix
hBx=boxchart(y,'MarkerStyle','none', ...    % do the box plot
               'BoxFaceColor', colors(i,:), ...
               'LineWidth', 0.5, ...
               'WhiskerLineStyle', '-');
hold on                       
hLmn=plot(1:size(y,2),mean(y), '*','r');    % and the stars for means
hAx=gca;
hAx.XTick=[];

Only two caveats:

each element in data is same number points; if this isn't so, will need to augment the shorter cells to length of longest with NaN, and
the data in each cell are column vectors--if rows, then transpose the y array before calling boxchart

You can stick with the existing way of generating an unneeded x variable to fake out barchart by giving an artificial grouping variable, but that's kinda' messy way. If they were going to write a new one, don't know why didn't allow for an x axis variable while at it other than simply the only grouping variable option.

N=numel(data);
colors = rand(N, 3);
figure;
hAx = axes();
hold on
for i=1:N
  boxchart(i*ones(size(data{i})), data{i},'MarkerStyle','none', ...
                                          'BoxFaceColor', colors(i,:), ...
                                          'LineWidth', 0.5, ...
                                          'WhiskerLineStyle', '-')
  plot(i,mean(data{i}),'*r')  % you didn't put in an x coordinate so all plotted at 1,mean(y)
end
set(gca,'xtick',[])

I'd recommend looking at vectorizing instead of the latter, though...

Related Solutions

MATLAB: Boxchart – many questions! Assign BoxFaceColors? separation lines? numeric xGroupData? Location of boxes? number of points

boxchart vs boxplot

>with r2020 there is finally a grouped boxplot called "boxchart".

The boxplot() function also has grouping options, has been around for much longer, and is often easier to customize than the newer standalone visualzation boxchart function.

ColorGroup & Notches

>How does one apply any property simultaneously to all boxes instead of looping? For instance like b.Notch = 'on' or a colormap to the ColorGroup?

See examples in the boxplot documentation for notches, and a description of ColorGroup.

If you want to use boxchart see the documentation regarding notches.

To apply changes to a group of handles to existing graphics objects, follow this example, although the loop you mentioned is also fine and just as fast (faster?),

h = boxchart(___);  % h is a vector of handles
set(h, {'BoxFaceColor'}, mat2cell(jet(numel(h)),ones(numel(h),1),3)) % jet is a colormap

Matlab documentation has a demo showing how to change colors in single bars or groups.

Separation lines

>How could I add separation lines?

For boxplot, use the FactorSeparator option.

For boxchart, this option currently doesn't exist (r2020b). If the x-axis is numeric, add divider lines using,

h = boxchart(__);
xline(x) % where x is the location of the line

If the x-axis is categorical it's a lot more complicated because divider lines cannot be added between categories. To add divider lines on a categorical x-axis you have to add additional categories to the x axis ticks, set their order, and then use xline() (or plot() or line()) with categorical x-values.

% Create boxchart showing 12 months of data
monthNum = randi(12,200,1);
data = rand(200,1)*100.*(normpdf(monthNum,6,1)+.25);
monthAbrv = categorical(monthNum,1:12,month(datetime(1, 1:12, 1), 's'));
figure()
h = boxchart(monthAbrv, data); 
% Separate seasons by divider lines
% First add categories to the x-axis
ax = h.Parent;  % axis handle
ax.XAxis.Categories' % view current categories.
ans = 1x12 cell array
    {'Jan'}    {'Feb'}    {'Mar'}    {'Apr'}    {'May'}    {'Jun'}    {'Jul'}    {'Aug'}    {'Sep'}    {'Oct'}    {'Nov'}    {'Dec'}
ax.XAxis.Categories = {
          'Jan' 'Feb' 'Spring',...
    'Mar' 'Apr' 'May' 'Summer',...
    'Jun' 'Jul' 'Aug' 'Fall',...
    'Sep' 'Oct' 'Nov' 'Winter',...
    'Dec'};
% Add xlines on seasonal categories
arrayfun(@(x)xline(x,'r-','LineWidth',1.5),categorical({'Spring','Summer','Fall','Winter'}))
% xline(__) for single lines
% if you want to label each line, 
% arrayfun(@(x)xline(x,'r-',x,'LineWidth',1.5),categorical({'Spring','Summer','Fall','Winter'}))
% If needed, removed seasonal tick labels
ax.XTickLabel([3,7,11,15]) = {''};

Fix overlapping boxes in boxchart

>Why can't I seem to get a correct looking diagram when plotting [with grouped data]?

Follow the examples in the documentation for boxchart and look for what's different in your setup.

You can fix the overlapping boxes by making the grouping variable categorical

boxchart(categorical(xgroupdata),ydata, 'GroupByColor', group);

Adding text labels

> I would like to be able to add a textlabel to any of the boxes

Use the text() function. See the bottom of this answer to learn how to get the x value of the boxplot centers.

For numeric axes it's as easy as using the text() function but for categorical axes, you must use categorical coordinates. This demo below shows the number of samples in each category and plots that number above the median lines.

% Produce boxchart
figure()
h = boxchart(randi(5,100,1),rand(100,1));
% compute median and number of samples for each box
[groupID, groups] = findgroups(h.XData);
medians = splitapply(@median,h.YData,groupID);
nSamples = splitapply(@numel,h.YData,groupID);
% Plot text
text(groups, medians, compose('n=%d',nSamples),...
    'HorizontalAlignment','Center','VerticalAlignment','bottom', ...
    'FontSize',8)

Extracting location of boxs

>I need to a) figure out the position of the boxes but I don't manage to understand the structure of the handle

Extracting the location of the boxes from the graphics handle involves accessing each graphics element and examining its coordinates. It's not easy but achievable with boxplot (see this answer). I haven't figured out a way to achieve this with boxchart as of r2020b.

Of course many of the parameters can be computed using the raw data.

The median marker are easy to get using,

h = boxchart(__);
[groupID, groups] = findgroups(h.XData);
medians = splitapply(@median,h.YData,groupID);

The upper and lower edges of the boxes are the 25th and 75th quartiles,

h = boxchart(__);
[groupID, groups] = findgroups(h.XData);
bounds = splitapply(@(y)quantile(y,[.25,.75]),h.YData,groupID);

The whisker ends are a bit more difficult. They mark the max/min values that are not outliers so first you have to compute the outlier thresholds. Outliers are any values that are greater than 1.5*IQR from the medians. IQR is computed for each box below. See documentation for more info.

h = boxchart(__);
[groupID, groups] = findgroups(h.XData);
IQR = splitapply(@iqr,h.YData,groupID);

The box centers and Left/Right edges for numeric axes are calculated using

h = boxchart(__);
boxCenters = unique(h.XData);
boxEdges = boxCenters(:) + h.BoxWidth.*[-1,1];  % for numeric matrices only

MATLAB: How to have more than one box plot in one plot

Please refer to my answer here: https://www.mathworks.com/matlabcentral/answers/392679-how-to-fill-boxes-in-boxplot-with-different-colors

Best Answer

Related Solutions

MATLAB: Boxchart – many questions! Assign BoxFaceColors? separation lines? numeric xGroupData? Location of boxes? number of points

MATLAB: How to have more than one box plot in one plot

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