[R] Two quick questions

[Serguei Kaniovski]

Hi all,

1. How to construct a date from three variables year, month, and day,
where all three are integers?

2. I have a dataframe by date and sector. I would like to add-up all
entries for all variable with identical date and sector, replacing the
original entries, i.e. emulate the STATA command "collapse (sum) var1
var2 var3, by(date sector)".

Thank you,
Serguei Kaniovski