Full join issue?

I want to check which object in which month no student in 12 months range. There 2 objects and each with 12 months in data set model (there are more than 30 objects and all in 12 months range in real). I want to insert rows to dataset area2021 (13273 rows), so each object has 12 months for each class and school. If a month exists, it means class having student; if a month is not there – means no student and insert from the model dataset. For example, in area2021 dataset, class_id 20981, obj_id Art-03, month 7,8,9,10 and 12 exist, after full join, I want to see the missing month 1,2,3,4,5,6,11 is added. Such should happen for every object in every class and every school. I thought that full join should do it because there are 12 months for objects in one dataset, but...Is there memory issue? How to archive this? Thanks a lots in advance!

model <-data.frame(
stringsAsFactors = FALSE,
year = c(2021,2021,2021,2021,2021,
month = c(1,2,3,4,5,6,7,8,9,10,
obj_cd = c("Math-01","Math-01","Math-01",
model$flag <- 'Y'

area2021 <- data.frame(
stringsAsFactors = FALSE,
school_id = c("10100","10100","10100",
class_id = c("20981","20981","20981",
obj_cd = c("Art-03","Art-03","Art-03",
year = c(2021,2021,2021,2021,2021,
month = c(7,8,9,10,12,4,5,6,7,8,
student_cnt = c(20,60,60,80,50,10,10,10,10,

full <- full_join(area2021,model,by=c('obj_cd','year','month')) %>%

They're added to the table but as NA values. What are you hoping to see?

You are right - this is not as what I thought. They 're added in the table, but not added under school, class, object group. Any thoughts? Thank you.

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