sum_up prints detailed summary statistics (corresponds
tab prints distinct rows with their count. Compared to
the dplyr function
count, this command adds frequency,
percent, and cumulative percent.
join is a wrapper for dplyr merge functionalities, with
two added functions
check checks there are no duplicates in
the master or using data.tables (as in Stata).
gen specifies the name of a new variable
that identifies non matched and matched rows (as in Stata).
update allows to update missing values of
the master dataset by the value in the using dataset