https://www.statmethods.net/r-tutorial/index.html
http://www.cookbook-r.com/
https://www.r-bloggers.com/
https://stackoverflow.com/tags/r/info
https://stackoverflow.com/questions/tagged/r-faq%20
read csv in R :
https://flowingdata.com/2015/02/18/loading-data-and-basic-formatting-in-r/
subsetting data:
https://www.statmethods.net/management/subset.html
ggplot2:
https://ggplot2.tidyverse.org/reference/theme.html
date formats in R:
https://www.r-bloggers.com/date-formats-in-r/
reshape the data:
https://seananderson.ca/2013/10/19/reshape/
http://www.cookbook-r.com/Manipulating_data/Converting_data_between_wide_and_long_format/
https://www.r-bloggers.com/melt/
https://s3.amazonaws.com/udacity-hosted-downloads/ud651/DataWranglingWithR.pdf
