MATLAB: How to make multiple boxplots in one axes

boxplotwhisker plot

I found this link regarding my question:

https://www.mathworks.com/help/stats/boxplot.html

for a sample data. But did not explain how those your data input should look like.

I found this pre-built function:

https://www.mathworks.com/matlabcentral/fileexchange/46545-alternative-box-plot#feedbacks

but I prefer to use standard mathwork function:

Any idea how to add inputs so like the one in the first link?

Best Answer

Here are several ways to add boxplots to an axis at specific x coordinates. The first two methods involve padding the input array with NaN values to offset the box plots along the x axis.

Add additional boxplots with matrix input.

Plot multiple boxplots with matrix input. One boxplot will be created per column.

% produce 6 boxplots at x = 1:6
cla()
boxplot(rand(5,3))

To horizontally offset the boxplots to start at x = n, pad n-1 columns of NaN values to the start of the matrix.

% Add two columns starting at x=4
hold on
data = rand(10,2); 
nanPad = nan(10,3); 
boxplot([nanPad, data])

Add additional boxplots with vector and grouping variable input

Plot multiple boxplots with a vector and a grouping variable.

cla()
x = 1:60;
group = repelem(1:3,1,20); 
boxplot(x,group)

To horizontally offset the boxplots to start at x = n, start the grouping variable at n and pad n-1 NaN values to the start of the first input vector. Assign the grouping variable values 1:n for those padded values.

hold on
data2 = 1:40;
group2 = repelem(4:5,1,20);     % grouping variable starts at n
% The rest of the code is adaptive.
nanPad = nan(1,min(group2)-1); 
boxplot([nanPad,data2],[1:min(group2)-1,group2])
axis tight 
xlim([min(xlim)-range(xlim)*.05, max(xlim)+range(xlim)*.05]) % +/- 5% of axis range

ylim([min(ylim)-range(ylim)*.05, max(ylim)+range(ylim)*.05]) % +/- 5% of axis range

Use the position property

This method has been recommended elsewhere but can be problematic. The demo below illustrates the problem of x tick label disappearing (r2019a).

boxplot(rand(1,200),repelem(1:2,1,100),'positions',[1,2], 'labels', [1,2])
hold on
boxplot(rand(1,200),repelem(3:4,1,100),'positions',[3,4], 'labels', [3,4])
axis tight

Related Solutions

MATLAB: Grouped boxplot with different lengths

You can vertically contatenate all of you data into a single column and use a [n x 2] grouping variable 'group' where group(:,1) identifies the G1, G2, G3 groups and group(:,2) identifies the column1 and column2 groups. Note that these groupings are also indicated in the x tick labels.

G1 = rand(108,2)-.5+[0,1]; 
G2 = rand(293,2)-.5+[2,4];
G3 = rand(30,2)-.5+[3,6]; 
group = [repelem([1;2;3],[numel(G1),numel(G2),numel(G3)]), ...
    [repelem([1;2],size(G1,1));repelem([1;2],size(G2,1));repelem([1;2],size(G3,1))]]; 
boxplot([G1(:);G2(:);G3(:)],group)

MATLAB: How to label a plot in Matlab with combine label

Option 1: use boxplotGroup()

See boxplotGroup() on the file exchange. If your boxplot data are matrices with the same number of columns, you can use this function to group them and provide primary and secondary labels.

Option 2: Use newline to create two rows of tick labels

Pro: Easy and clean

Con: Less control of the alignment between the upper and lower labels.

ax = axes(); 
xlim([0,12])
ticks = {'a_peaks','b','a_concat','b','a_F0','b','a_Fs','b'};
ticks = strrep(ticks,'_','\newline'); % replace underscore with \newline

ax.XTick = [1 2 4 5 7 8 10 11]; 
ax.XTickLabel = ticks;

This variation below controls the alignment between the upper and lower labels but adds an additional tick between the upper labels.

ax = axes(); 
xlim([0,12])
ticks = {'a','_peaks','b','a','_concat','b','a','_F0','b','a','_Fs','b'};
ticks = strrep(ticks,'_','\newline'); % replace underscore with \newline
ax.XTick = [1 1.5 2   4 4.5 5   7 7.5 8   10 10.5 11]; 
ax.XTickLabel = ticks;

Option 2.1: Use cell array with justified text

Added to answer 11-Feb-2021

Pro: Intuitive label arrangement & text justification

ax = axes(); 
xlim([0,12])
ticks = {'a','','b','a','','b','a','','b','a','','b'; ...    % 1st row of labels
    '','peaks','','','concat','','','F0','','','Fs',''};  % 2nd row of labels
ticksJust = strjust(pad(ticks),'center'); % Justify: 'left'(default)|'right'|'center
% ticksJust =
%   2×9 cell array
%     {'  a  '} {'     '} {'  b  '} {'  a  '} {'     '} {'  b  '} {'  a  '} {'     '} {'  b  '}
%     {'     '} {'peaks'} {'     '} {'     '} {'peaks'} {'     '} {'     '} {'peaks'} {'     '}
tickLabels = strtrim(sprintf('%s\\newline%s\n', ticksJust{:}));
ax.XTick = [1 1.5 2   4 4.5 5   7 7.5 8   10 10.5 11]; 
ax.XTickLabel = tickLabels;

Option 3: Use text() to create a second row of tick lables

Pro: More control over the placement of the tick labels.

Con: Axis limits must be set and the lower tick labels will move if the pan feature is used.

ax = axes(); 
% Set axis limits before labeling
xlim([0,12])
ylim([0,1]); 
% Shorten the height of the axes to 90% and shift  
% upward to make room for the 2-layers of labels.
upperPosition = sum(ax.Position([2,4])); 
ax.Position(4) = ax.Position(4) * .9; 
ax.Position(2) = minus(upperPosition, ax.Position(4)); 
% label the upper row using xtick and xticklabel
ax.XTick = [1 2 4 5 7 8 10 11]; 
ax.XTickLabel = {'a' 'b'}; 
% use text() to creat the lower row of tick labels
% The 2nd layer will be 6% of the y axis range below the axis.
lowerLevel = min(ylim(ax))-range(ylim(ax))*.06; 
lowerLabels = {'peaks','concat','F0','FS'}; 
text([1.5, 4.5, 7.5, 10.5], repmat(lowerLevel,1,numel(lowerLabels)), lowerLabels,...
    'VerticalAlignment','Top','HorizontalAlignment','Center')

Best Answer

Related Solutions

MATLAB: Grouped boxplot with different lengths

MATLAB: How to label a plot in Matlab with combine label

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