Using this it gives the date time format to the specific column
df[,":="(date = as.numeric(as.POSIXct(date , "%Y-%m-%d %H:%M:%S"))]
How is it possible to convert a date column to a epoch/unix date column like this it can be for one value
as.numeric(as.POSIXct("2013-09-16 2:13:46 EST"))