Thank you very much for this wonderful sharing!!

我购买了你的附件，却没有发现数据，其实没法按你的材料进行学习。可否同时提供数据？否则，对读者就没什么意义了。谢谢。

Thank you for your suggestions.  All I consider in this edition is the cream part of organizing the data frame. It's very practical and saves me a lot of time in processing data if the contents can be digested properly.  One of the weakness in this edition is that it doesn't provide data that you can cut and paste in your R studio right away.  Although the zip file contains the codes, it might be not enough for new beginner to start immediately. There are three solutions.  First, I will gradually improve this file. Will you wait for me?   Second, you can use the data that R provides, such as cats, co2 and etc.,  or refer to website (https://stat.ethz.ch/R-manual/R-patched/library/datasets/html/00Index.html).  There are immense data source in R. You can practice what you learn from my file  based on these data.  Third, type the code in searching engine. I'm sure there are a lot of learners like you to explore the beauty in R.  Don't be frustrated and try it.  You will love it, enjoy it.      

累不累？