PCA-based Category Encoder for Categorical to Numerical Variable Conversion

Increasing the cardinality of categorical variables might decrease the overall performance of ML algorithms. This paper presents a novel computational preprocessing method to convert categorical to numerical variables for machine learning (ML) algorithms. In this method, We select and convert three categorical features to numerical features. First, we choose the threshold parameter based on the distribution of categories in variables. Then, we use conditional probabilities to convert each categorical variable into two new numerical variables, resulting in six new numerical variables in total. After that, we feed these six numerical variables to the Principal Component Analysis (PCA) algorithm. Next, we select the whole or partial numbers of Principal Components (PCs). Finally, by applying binary classification with ten different classifiers, We measured the performance of the new encoder and compared it with the other 17 well-known category encoders. The proposed technique achieved the highest performance related to accuracy and Area under the curve (AUC) on high cardinality categorical variables using the well-known cybersecurity NSLKDD dataset. Also, we defined harmonic average metrics to find the best trade-off between train and test performance and prevent underfitting and overfitting. Ultimately, the number of newly created numerical variables is minimal. Consequently, this data reduction improves computational processing time which might reduce processing data in 5G future telecommunication networks.