plot

Plot clustering evaluation object criterion values

Syntax

plot(evaluation)

plot(ax,evaluation)

h = plot(___)

Description

plot(evaluation) displays a plot of the criterion values versus the number of clusters, based on the values in the clustering evaluation object evaluation.

plot(ax,evaluation) plots into the axes specified by ax instead of the current axes (gca). (since R2024a)

h = plot(___) returns a Line object using any of the input argument combinations in the previous syntaxes. Use this object to inspect and adjust the properties of the plot line. For a list of properties, see Line Properties.

Examples

Plot Clustering Evaluation Criterion Values

Plot the criterion values versus the number of clusters for each clustering solution stored in a clustering evaluation object.

Load the fisheriris data set. The data contains length and width measurements from the sepals and petals of three species of iris flowers.

load fisheriris

Create a clustering evaluation object. Cluster the data using kmeans, and evaluate the optimal number of clusters using the Calinski-Harabasz criterion.

rng("default") % For reproducibility
evaluation = evalclusters(meas,"kmeans","CalinskiHarabasz","KList",1:6);

Plot the Calinski-Harabasz criterion values for each number of clusters tested.

plot(evaluation)

The plot shows that the highest Calinski-Harabasz value occurs at three clusters, suggesting that the optimal number of clusters is three.

Plot Optimal Number of Clusters Using Different Criteria

Cluster data using each of the four clustering evaluation criteria. For each criterion, create a plot of the criterion values and indicate the optimal number of clusters.

Generate sample data containing random numbers from three multivariate distributions with different parameter values.

rng("default") % For reproducibility
n = 200;

mu1 = [2 2];
sigma1 = [0.9 -0.0255; -0.0255 0.9];

mu2 = [5 5];
sigma2 = [0.5 0; 0 0.3];

mu3 = [-2 -2];
sigma3 = [1 0; 0 0.9];

X = [mvnrnd(mu1,sigma1,n); ...
     mvnrnd(mu2,sigma2,n); ...
     mvnrnd(mu3,sigma3,n)];

Cluster the data using kmeans, and evaluate the optimal number of clusters using the Calinski-Harabasz, Davies-Bouldin, gap, and silhouette criteria.

calinskiEvaluation = evalclusters(X,"kmeans","CalinskiHarabasz", ...
    "KList",1:6);
daviesEvaluation = evalclusters(X,"kmeans","DaviesBouldin", ...
    "KList",1:6);
gapEvaluation = evalclusters(X,"kmeans","gap","KList",1:6);
silhouetteEvaluation = evalclusters(X,"kmeans","silhouette", ...
    "KList",1:6);

For each clustering evaluation object, plot the criterion values for the number of proposed clusters. In each plot, change the color of the plot line and add a vertical line indicating the optimal number of clusters.

t = tiledlayout(2,2);
title(t,"Optimal Number of Clusters for Different Criteria")
colors = lines(4);

% Calinski-Harabasz Criterion Plot
nexttile
h1 = plot(calinskiEvaluation);
h1.Color = colors(1,:);
hold on
xline(calinskiEvaluation.OptimalK,"--","Optimal K", ...
    "LabelVerticalAlignment","middle")
hold off

% Davies-Bouldin Criterion Plot
nexttile
h2 = plot(daviesEvaluation);
h2.Color = colors(2,:);
hold on
xline(daviesEvaluation.OptimalK,"--","Optimal K", ...
    "LabelVerticalAlignment","middle")
hold off

% Gap Criterion Plot
nexttile
h3 = plot(gapEvaluation);
h3.Color = colors(3,:);
hold on
xline(gapEvaluation.OptimalK,"--","Optimal K", ...
    "LabelVerticalAlignment","middle")
hold off

% Silhouette Criterion Plot
nexttile
h4 = plot(silhouetteEvaluation);
h4.Color = colors(4,:);
hold on
xline(silhouetteEvaluation.OptimalK,"--","Optimal K", ...
    "LabelVerticalAlignment","middle")
hold off

The four plots indicate that the optimal number of clusters is three, regardless of the clustering criterion.

Input Arguments

ax — Target axes

Axes object

Target axes, specified as an Axes object. If you do not specify the axes, then plot uses the current axes (gca).

evaluation — Clustering evaluation data

CalinskiHarabaszEvaluation object | DaviesBouldinEvaluation object | GapEvaluation object | SilhouetteEvaluation object

Clustering evaluation data, specified as a CalinskiHarabaszEvaluation, DaviesBouldinEvaluation, GapEvaluation, or SilhouetteEvaluation clustering evaluation object. Create a clustering evaluation object by using evalclusters.

Version History

Introduced in R2013b

R2024a: Specify target axes

Specify the target axes for the plot by using the ax input argument.