How to convert data from an Excel spreadsheet into the ARFF format for use in machine learning applications? ARFF (Attribute-Relation File Format) is an ASCII file format used by the WEKA machine learning software. It is a text file and contains a header section, a data section, and an optional comment section. The header section describes the data set and the data section contains the actual data. Converting an Excel spreadsheet into the ARFF format is a relatively simple process. The first step is to save the Excel file as a .csv file. Then, the .csv file can be opened in a text editor and the necessary changes can be made to convert it into the ARFF format. Finally, the ARFF file can be saved and used in machine learning applications.