Reorganize the code for R

Overall work flow:

-/reference/

1. Some code from previous study in 'Data Science' course of coursera

2. Some code from Hadley Wickham's books ('R for Data Science' and 'Advance R')

3. Other code by my own or online open resource

-/html/

1. Standardized_workflow_for_rmarkdown.Rmd

2. Visulization.Rmd

3. vapply-tapply.Rmd

4. lapply-sapply.Rmd

5. input_outout_data.Rmd

6. function.Rmd

-/code-book/

1. Standardized_workflow_for_rmarkdown.Rmd

2. Visulization.Rmd

3. vapply-tapply.Rmd

4. lapply-sapply.Rmd

5. input_outout_data.Rmd

6. function.Rmd

-/graph/

-/rdata/

1. flags.txt from swirl

-/url/

purrr https://www.r-bloggers.com/lesser-known-purrr-tricks/

broom

https://cran.r-project.org/web/packages/broom/vignettes/broom.html