returning an empty matrix in step 4

[v14sta]

Hi, I have actually faced an issue in running step 4 of this tutorial, which is an empty matrix. It seems that the code cant catches the data frame and data that is merged in previous chunks. Although I run the previous steps correctly and got the results as it is indicated in the tutorial. But I can't see what is the problem that it does not work. I hope you could assist me where I have gone wrong.