Find Change Points

Find abrupt changes in data in the Live Editor

Description

The Find Change Points task lets you interactively find abrupt changes in the mean, variance, or slope and intercept of data. The task automatically generates MATLAB^® code for your live script.

Using this task, you can:

• Specify the change point type and locate the change points in data in a workspace variable.

• Adjust the number of detected change points.

• Visualize change point locations and the segments of data between them.

For more information on Live Editor tasks, see Add Interactive Tasks to a Live Script.

Related Functions

Find Change Points generates code that uses the ischange function.

Open the Task

To add the Find Change Points task to a live script in the MATLAB Editor:

• On the Live Editor tab, select Task > Find Change Points.

• In a code block in the script, type a relevant keyword, such as change, find, variance, or linear. Select Find Change Points from the suggested command completions. For some keywords, the task automatically updates one or more corresponding parameters.

Examples

Change in Linear Regime

Interactively find abrupt changes in the slope and intercept of data using the Find Change Points task in the Live Editor.

Create a vector of noisy data. Create a plot to visualize the data.

data = [zeros(1,100) 1:100 99:-1:50  50*ones(1,250)] + 10*rand(1,500);
plot(1:500,data)

Open the Find Change Points task in the Live Editor. To find abrupt changes in the slope and intercept of the vector, select data as the input data.

In the Specify parameters section of the task, in the Type of change field, specify the change detection method as Linear. To reduce the number of change points detected due to noise, increase the change point threshold to 100. Alternatively, you can specify the maximum number of change points to detect.

To view the segments between change points more clearly, remove the input data from the plot by clearing the Input data field in the Display results section.

Related Examples

• Add Interactive Tasks to a Live Script
• Clean Messy Data and Locate Extrema Using Live Editor Tasks

Parameters

Input data — Valid input data from workspace

vector | table | timetable

This task operates on input data contained in a vector, table, or timetable. The data can be of type single or double.

For table or timetable input data, to clean all variables of type single or double, select All supported variables. To choose which single or double variables to clean, select Specified variables.

Type of change — Change detection method

mean | variance | linear

Specify the method for detecting changes in the input data as one of these options.

Method	Description
mean	Find abrupt changes in the mean of the data.
variance	Find abrupt changes in the variance of the data.
linear	Find abrupt changes in the slope and intercept of the data.

Version History

Introduced in R2019b

R2022b: Plot multiple table variables

Simultaneously plot multiple table variables in the display of this Live Editor task. For table or timetable data, to visualize all selected table variables at once in a tiled chart layout, set the Variable to display field.

R2022b: Specify tabular output

Output a table or timetable with logical variables corresponding to the table variables checked for change points, or append the logical variables to the input table. For table or timetable input data, to specify the tabular format, set the Output format field.

R2022a: Live Editor task does not run automatically if inputs have more than 1 million elements

This Live Editor task does not run automatically if the inputs have more than 1 million elements. In previous releases, the task always ran automatically for inputs of any size. If the inputs have a large number of elements, then the code generated by this task can take a noticeable amount of time to run (more than a few seconds).

When a task does not run automatically, the Autorun indicator is disabled. You can either run the task manually when needed or choose to enable the task to run automatically.

R2021a: Operate on multiple table variables

This Live Editor task can operate on multiple table variables at the same time. For table or timetable input data, to operate on multiple variables, select All supported variables or Specified variables. Return all of the variables or only the modified variables, and specify which variable to visualize.