Having a character date column in data frame. I want 8 quarter's data from a desired quarter - 2021-01(1q21)
and count backwards inclusively: 2021-7(3q21) to 2019-10(4q19). how to do it efficiently? Thanks in advance!
prod_id <- c(21,21,21,20,20,20,20,19,19,19,19,18,18,18,18)
start_date <- c('2021-01-1','2021-04-1','2021-07-1',
'2020-01-1','2020-04-1','2020-07-1','2020-10-1',
'2019-01-1','2019-04-1','2019-07-1','2019-10-1',
'2018-01-1','2018-04-1','2018-07-1','2018-10-1')
prod <- data.frame(prod_id, start_date, stringsAsFactors=FALSE) %>% filter(???)