add data label to a grouped bar chart in matlab - matlab

Question

I'd like to add data to a grouped bar chart in matlab. However, I can't place each data in the top of each bar. Using this question for usual bar and this one, I tried the following code for grouped chart, but xpos and ypos is not correct. Any help is appreciated.
a=[0.92,0.48,0.49];
b=[0.74,0.60,0.30];
c=[0.70,0.30,0.10];
X=[a;b;c];
hbar = bar(X, 'grouped');
for i=1:length(hbar)
XDATA=get(hbar(i),'XData')';
YDATA=get(hbar(i),'YData')';
labels = cellstr(num2str(YDATA));
ygap=0.01;
for j=1:size(XDATA,2)
xpos=XDATA(i,1);
ypos=YDATA(i,1)+ygap;
t=[num2str(YDATA(1,j),3)];text(xpos,ypos,t,'Color','k','HorizontalAlignment','left','Rotation',90)
end
end

Answer 1

There are two main errors in your code:
the definition of the inner loop: XDATA is a (N x 1) array therefore the inner loop makes only one iteration since size(XDATA,2) is 1. This makes your labels added on the center bar of each group
in the innser loop you first set the variable t as the label (t=[num2str(YDATA(1,j),3)];; then you use the same variable as output of the text function (t = text(xpos,ypos,labels{i});; then you use that variable in another call to text but now it contains the handle to the label and no longer the label string. This generate an error.
To proper add the labels you have to modify your code in order to identify the X position of the label.
You have to retreive the position of each bar within the groups: the X position of each bar is given by its XDATA value, plus its offset with respect to the center of the group. The offset value is stored in the XOffset property of the bar (notice: this is an hidden / undocumented property).
This is a possible implementation:
% Generate some data
bar_data=rand(4,4)
% Get the max value of data (used ot det the YLIM)
mx=max(bar_data(:))
% Draw the grouped bars
hbar=bar(bar_data)
% Set the axes YLIM (increaed wrt the max data value to have room for the
% label
ylim([0 mx*1.2])
grid minor
% Get the XDATA
XDATA=get(hbar(1),'XData')';
% Define the vertical offset of the labels
ygap=mx*0.1;
% Loop over the bar's group
for i=1:length(hbar)
% Get the YDATA of the i-th bar in each group
YDATA=get(hbar(i),'YData')';
% Loop over the groups
for j=1:length(XDATA)
% Get the XPOS of the j-th bar
xpos=XDATA(j);
% Get the height of the bar and increment it with the offset
ypos=YDATA(j)+ygap;
% Define the labels
labels=[num2str(YDATA(j),3)];
% Add the labels
t = text(xpos+hbar(i).XOffset,ypos,labels,'Color','k','HorizontalAlignment','center','Rotation',90)
end
end
Hope this helps,
Qapla'