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Plot Categorical Data

This example shows how to plot data from a categorical array.

Load Sample Data

Load sample data gathered from 100 patients.

load patients

  Name                            Size            Bytes  Class      Attributes

  Age                           100x1               800  double               
  Diastolic                     100x1               800  double               
  Gender                        100x1             12212  cell                 
  Height                        100x1               800  double               
  LastName                      100x1             12416  cell                 
  Location                      100x1             15008  cell                 
  SelfAssessedHealthStatus      100x1             12340  cell                 
  Smoker                        100x1               100  logical              
  Systolic                      100x1               800  double               
  Weight                        100x1               800  double               

Create Categorical Arrays from Cell Arrays of Strings

The workspace variable, Location, is a cell array of strings that contains the three unique medical facilities where patients were observed.

To access and compare data more easily, convert Location to a categorical array.

Location = categorical(Location);

Summarize the categorical array.

     County General Hospital        39 
     St. Mary's Medical Center      24 
     VA Hospital                    37 

39 patients were observed at County General Hospital, 24 at St. Mary's Medical Center, and 37 at the VA Hospital.

The workspace variable, SelfAssessedHealthStatus, contains four unique values, Excellent, Fair, Good, and Poor.

Convert SelfAssessedHealthStatus to an ordinal categorical array, such that the categories have the mathematical ordering Poor < Fair < Good < Excellent.

SelfAssessedHealthStatus = categorical(SelfAssessedHealthStatus,...
    {'Poor' 'Fair' 'Good' 'Excellent'},'Ordinal',true);

Summarize the categorical array, SelfAssessedHealthStatus.

     Poor           11 
     Fair           15 
     Good           40 
     Excellent      34 

Plot a Histogram

Create a histogram bar plot directly from a categorical array.

title('Self Assessed Health Status')

The function hist accepts the categorical array, SelfAssessedHealthStatus, and plots the category counts for each of the four categories.

Create a histogram of the hospital location for only the patients who assessed their health as Fair or Poor.

title('Location of Patients in Fair or Poor Health')

Create a Pie Chart

You can use the numeric output from the countcats function to create other types of plots.

Create a pie chart of the self assessed health status of the 100 patients.

h = pie(countcats(SelfAssessedHealthStatus));
title('Self Assessed Health Status From 100 Patients')

% Add the category names to the pie chart labels. Use strcat to prepend
% the category names to the percentage labels.
textObjs = findobj(h,'Type','text');
oldStr = get(textObjs,{'String'});


Create a Scatter Plot

Convert the cell array of strings to a categorical array.

Gender = categorical(Gender);

Summarize the categorical array, Gender.

     Female      53 
     Male        47 

Gender is a 100-by-1 categorical array with two categories, Female and Male.

Use the categorical array, Gender, to access Weight and Height data for each gender separately.

X1 = Weight(Gender=='Female');
Y1 = Height(Gender=='Female');

X2 = Weight(Gender=='Male');
Y2 = Height(Gender=='Male');

X1 and Y1 are 53-by-1 numeric arrays containing data from the female patients.

X2 and Y2 are 47-by-1 numeric arrays containing data from the male patients.

Create a scatter plot of height vs. weight. Indicate data from the female patients with a circle and data from the male patients with a cross.

h1 = scatter(X1,Y1,'o');
hold on
h2 = scatter(X2,Y2,'x');

title('Height vs. Weight')
xlabel('Weight (lbs)')
ylabel('Height (in)')

See Also

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