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