stop("Not sure this is needed")  


-------------------------------------------



DB.raw2 <- DB.rawT # [artist %in% c("Jessy Lanza", "Fleshgod Apocalypse")]

  START.TIME <- proc.time()
  setkey(DB.raw2, userid, download_datetime)
  
  DB.raw2[ , usrFirstTimeOnTrack  := FALSE]
  DB.raw2[ , usrFirstTimeOnUPC    := FALSE]
  DB.raw2[ , usrFirstTimeOnArtist := FALSE]
  
  s.t( DB.raw2[DB.raw2[, .I[[1L]], by=list(userid, trackid)]$V1, usrFirstTimeOnTrack := TRUE], "Calc User First, by trackid")
  s.t( DB.raw2[DB.raw2[, .I[[1L]], by=list(userid, upc)]$V1, usrFirstTimeOnUPC := TRUE], "Calc User First, by upc")
  s.t( DB.raw2[DB.raw2[, .I[[1L]], by=list(userid, artist)]$V1, usrFirstTimeOnArtist := TRUE], "Calc User First, by artist")

  END.TIME <- proc.time()
  cat("\n\nTOTAL TIME:\n")
  print(END.TIME - START.TIME)

setkeyIfNot(DB.raw2, "upc", "download_date")


weeks <- c(2, 6)
measuringBy1 <- list("upc")  # ignoring for now:   , "artist")
measuringBy2 <- list(NULL, "user_country", "mkt_priority", c("user_country", "mkt_priority"))  
include <- c("SpotifyAddRan")   #, "rel_month")

are(DB.raw2)

## THIS IS THE for-loop I AM COMBINING USING expand.grid & lapply
# for (W in weeks) 
#   for (M1 in measuringBy1)
#     for (M2 in measuringBy2) {
#       DB.raw2[(download_date >= startDate) & (download_date < startDate + (W*7))
#         , list(
#              count     = c(.N, sum(usrFirstTimeOnUPC))
#             , measuring = paste0(c("total.by.", "unique.by."), paste(c(M1, M2), collapse=".by."))
#             , timeframe = sprintf("%02d weeks", W)
#           )
#         , by = c(M1, M2) 
#     ]
#   }

DT.list <- 
  apply(expand.grid(W=weeks, M1=measuringBy1, M2=measuringBy2), 1, function(X)
       DB.raw2[(download_date >= startDate) & (download_date < startDate + (X$W*7))
         , list(
              count     = c(.N, sum(usrFirstTimeOnUPC))  # the sum needs to change depending on W1
             , measuring = paste0(c("total.by.", "unique.by."), paste(c(X$M1, X$M2), collapse=".by."))
             , timeframe = sprintf("%02d weeks", X$W)
           )
         , by = c(include, X$M1, X$M2) 
     ]
  )

setattr(DT.list, "names", sapply(DT.list, function(DT) DT[1, gsub("^(total|unique)\\.", "", measuring)]))

DT.list[1:5]