Assessments /Getting and Cleaning Data Course Project

The file describing how the script works.
*The data obtained from:
http://archive.ics.uci.edu/ml/datasets/Human+Activity+Recognition+Using+Smartphones
the data for the project:
https://d396qusza40orc.cloudfront.net/getdata%2Fprojectfiles%2FUCI%20HAR%20Dataset.zip
*steps:

1. import library data.table
2. the files are stored in directory named Dataset. Get X_train,y_train,subject_train from directory ./Dataset/train, and then get test data respectively.
3. use rbind to merge the training and the test sets, and create one data set.
4. read features from "./Dataset/features.txt"
5. use setnames from data.table to set names of the dataset X_all
6. use grep to get columns which names contain "mean" and "std"
7. extract these columns and saved in X_all1
8. read descriptive activity names from "./Dataset/activity_labels.txt", and use it to change y_all, and saved as y_all1.
9. get the tidydata needed, and change their names appropirately.
10. save tidydata to tidydata.txt
11. use aggregate to get a new tidy data set with the average of each variable for each activity and each subject, name it tidymean
12. save tidymean to tidymean.txt