+## create list of folks who are missing in class
+missing.in.class <- call.list.full[is.na(call.list.full$answered) |
+ (!is.na(call.list.full$answered) & !call.list.full$answered),
+ c("discord.name", "day")]
+
+missing.in.class <- unique(missing.in.class)
+
+setDT(attendance)
+setkey(attendance, discord.name, day)
+setDT(missing.in.class)
+setkey(missing.in.class, discord.name, day)
+
+## drop presence for people on missing days
+attendance[missing.in.class,]
+attendance <- as.data.frame(attendance[!missing.in.class,])
+