r data.table条件和引用/从另一个单独的data.table执行查找

我是R和data.tables的初学者，但我已经读了足够多的书，确信它们对于大型数据集的速度/效率。我到处找，找不到我认为容易的问题的答案

问题是：给定两个数据表DT1和DT2

DT1 <- data.table(AA=c("A","B","C","A","B","C","A","B","C","A","B","C"),
                  BB=c(35,45,25,25,85,15,55,55,95,35,25,75)
                  )

DT2 <- data.table(CC=c("A","B","C","A","B","C"),
                  DD=c(10,20,30,40,50,60),
                  EE=c(5,5,10,10,15,20)
                  )

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在NewCol的每个单元格中复制。我不想把这篇文章和两个Excel表格混在一起，显然Excel并不是很好，因为有很多原因，但如果在Excel中这么简单，那么在R data.tables中也一定相当简单，对吧？

在最新的

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希望得到的联接列的命名在将来会变得更加合理，因为现在只需使用

setnames

就可以了！！！谢谢你，埃迪！！！对于那些正在努力安装1.9.7的人（我在Windows环境中），我发现在安装Rtools时必须选择“编辑路径”选项才能使其正常工作。我重新启动了。

DT1_DesiredOutput <- data.table(AA=c("A","B","C","A","B","C","A","B","C","A","B","C"),
                                BB=c(35,45,25,25,85,15,55,55,95,35,25,75),
                                NewCol=c(10,15,30,10,0,30,0,0,0,10,15,0)
                                )

{=SUM(IF( ($F$7:$F$12=B7)*($G$7:$G$12>C7), $H$7:$H$12))}

DT2[DT1, on = .(CC = AA, DD >= BB), .(NewCol = sum(EE, na.rm = T)), by = .EACHI]
#    CC DD NewCol
# 1:  A 35     10
# 2:  B 45     15
# 3:  C 25     30
# 4:  A 25     10
# 5:  B 85      0
# 6:  C 15     30
# 7:  A 55      0
# 8:  B 55      0
# 9:  C 95      0
#10:  A 35     10
#11:  B 25     15
#12:  C 75      0