This part of the code is used to do gait-extraction training, corresponding to Dataset #7 and Dataset #8.
In these two data sets, each samlpe has 1024 rows, that is, the data length in the time series is 1024. 
There are 6 columns in each row. The first three columns are the data of the X, Y, and Z axes of the accelerometer, and the last three columns are the data of the X, Y, and Z axes of the gyroscope.