Graphics

Pie Charts

Pie charts display the percentage that each element in a vector or matrix contributes to the sum of all elements. pie and pie3 create 2-D and 3-D pie charts.

Example - Pie Chart

Here is an example using the pie function to visualize the contribution that three products make to total sales. Given a matrix X where each column of X contains yearly sales figures for a specific product over a five-year period,

X = [19.3 22.1 51.6;
     34.2 70.3 82.4;
     61.4 82.9 90.8;
     50.5 54.9 59.1;
     29.4 36.3 47.0];

sum each row in X to calculate total sales for each product over the five-year period.

x = sum(X);

You can offset the slice of the pie that makes the greatest contribution using the explode input argument. This argument is a vector of zero and nonzero values. Nonzero values offset the respective slice from the chart.

First, create a vector containing zeros.

explode = zeros(size(x));

Then find the slice that contributes the most and set the corresponding explode element to 1.

[c,offset] = max(x);
explode(offset) = 1;

The explode vector contains the elements [0 0 1]. To create the exploded pie chart, use the statement.

h = pie(x,explode); colormap summer

Labeling the Graph

The pie chart's labels are text graphics objects. To modify the text strings and their positions, first get the objects' strings and extents. Braces around a property name ensure that get outputs a cell array, which is important when working with multiple objects.

textObjs = findobj(h,'Type','text');
oldStr = get(textObjs,{'String'});
val = get(textObjs,{'Extent'});
oldExt = cat(1,val{:});

Create the new strings, then set the text objects' String properties to the new strings.

Names = {'Product X: ';'Product Y: ';'Product Z: '};
newStr = strcat(Names,oldStr);
set(textObjs,{'String'},newStr)

Find the difference between the widths of the new and old text strings and change the values of the Position properties.

val1 = get(textObjs, {'Extent'});
newExt = cat(1, val1{:});
offset = sign(oldExt(:,1)).*(newExt(:,3)-oldExt(:,3))/2;
pos = get(textObjs, {'Position'});
textPos =  cat(1, pos{:});
textPos(:,1) = textPos(:,1)+offset;
set(textObjs,{'Position'},num2cell(textPos,[3,2]))

Comparing Datasets with Area Graphs

Removing a Piece from a Pie Charts