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我有两个data.table我想加入的(形成笛卡尔积).其中一个data.tables键入一个Date向量,另一个键入numeric向量:

# data.table with dates (as numeric)
dtDates2 = data.table(date = 
                       as.numeric(seq(from = as.Date('2014/01/01'), 
                           to = as.Date('2014/07/01'), by = 'weeks')),
                     data1 = rnorm(26))

# data.table with dates
dtDates1 = data.table(date = 
                        seq(from = as.Date('2014/01/01'), 
                            to = as.Date('2014/07/01'), by = 'weeks'),
                      data1 = rnorm(26))


# data.table with customer IDs
dtCustomers = data.table(customerID = seq(1, 100),
                      data2 = rnorm(100))

我setkey尝试使用CJ以下方式交叉加入它们:

# cross join the two datatables
setkey(dtCustomers, customerID)
setkey(dtDates1, date) …