Each .csv contains a set of data points (say, from column 4, where rows 4, 5 and 9 are individual subjects of the graph) that I want to plot with the date along the X axis. Basically, what I want to ...

See how to join two data sets by one or more common columns using base R’s merge function, dplyr join functions, and the speedy data.table package. R has a number of quick, elegant ways to join data ...