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Classification Learner App in MATLAB 

 December 21, 2020

By  Roshini

We used the J, M, and V letter datasets for a classification task in the previous blog. We performed the classification by directly coding. Now let us see how we can do it in the Classification Learner app. In coding, we used only the KNN method, and we did not try to improve accuracy. But in the app, we can use Classification Learner to train models of these classifiers: decision trees, discriminant analysis, support vector machines, logistic regression, nearest neighbors, naive Bayes, and ensemble classification. In addition to training models, we can explore the data, select features, specify validation schemes, and evaluate results. We can export a model to the workspace to use the model with new data or generate MATLAB code to learn about programmatic classification.

The following are the steps that we will be following to perform classification in the Classification Learner app:

1) Our first step before we open the app will be to import the data we will use in the workspace. I have used the same data features of “J”, “M” and “V” that I had used in the previous blog of classification learning. The features.xlsx file that contains the data has been extracted to the workspace.

2) Now, we have to click the classification learner available in the Apps tab in MATLAB. It will be automatically available if you have installed the Statistics and Machine Learning toolbox. We can also open the app by entering classificationLearner in the command prompt.

App

3) This is how the app looks like after opening. To start the session, we need to click on the New Session icon.

new-session

4) A new window named New Session will open. Since the data is already in the workspace, it will be shown in the option, and we have to select it.

start-session

As the features are selected in the dataset part, it will automatically identify the response and predictors. The response indicated here is the parameter into which we will classify the data. Here, since the Character is selected as the response and it shows it has three unique values that are “J”, “M” and “V”. Predictors are the features that we use to classify them into the respective classes. The other two columns that are Aspect Ratio and Duration, will automatically become the predictors.

Before going into the validation part, we shall see what validation is and its parts. In validation, the training data is divided into training and validation parts. The validation part is used to check the trained model before testing to see that the model doesn’t get overfitted. There are two different types of validation processes:

  1. Cross-Validation: In this, the number of folds is the number of parts the training data will randomly divide. One part of it will be used for validation and the remaining for training.

  2. Holdout Validation: We can select the percentage of data held out as a testing dataset and the remaining for training. This is usually recommended for large datasets.

Since the dataset that I am using is small, I am not using validation. If I use validation, then, the training data will not be sufficient to learn.

5) This is how the app will look after selecting the dataset and validation method. Initially, the scatter plot of the training data features will appear as the session is opened. The X and Y-axis of the scatter plot can be changed on the right side.

scatter plot

6) Since we don’t know which model suits the dataset, we will select all options here. After this, we have to click the train option to train the testing data for all available models.

train

7) We can see the training accuracy results for 24 models on the left side. And there is the scatter plot in the center for the model predictions for the selected model.

best model

8) There is an icon called plots that has the following options.

plot

9) We can now select the top accuracy model. Here we have Fine KNN and Weighted KNN having the highest accuracy of 99.2%. Click on the Export option, and I have exported each of it to the workspace as trainedModel and trainedModel1. Export has the following options:

export

10) We can test these two models on the testing data and check the accuracy to find the best model. 

After exporting, the command window will look like this:

command

The trainedModel.predictFcn(readtable(“features.xlsx”)) command will be used to get the prediction output of the exported model. The following code is used to find the accuracy of the model.

testdata=readtable("testdata.xlsx")

predictions = char(trainedModel.predictFcn(testdata))

% accuracy

iscorrect=predictions==cell2mat(string((testdata.Character)))

iscorrect=iscorrect(:,2)

accuracy = sum(iscorrect)*100/20

accuracy

Similarly, we have to try for the remaining exported model also. Finally, we get the testing accuracy of 90% and 85% for Fine KNN and weighted KNN models. Hence, we can use Fine KNN as it is the best model for this dataset. Thus, in this way, we will find out the best model for the dataset in less time. When we directly coded using the KNN model, we got an accuracy of 80%. Using the app, we were able to identify the best model quickly and got a better accuracy of 90%.

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About the author 

Roshini

An Electronics and Communication engineering student. Passionate about learning and sharing with others.

  • Mihir Rana says:

    Good concept and interesting blog.

  • Isra Nenwo says:

    Undefined function ‘string’ for input arguments of type ‘cell. What do i do about this pls?

  • tanu jain says:

    tanu
    it is good for classification for algorithm based machine learning …by direct importing excel or any data

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