根据另一个data.table的行提取data.table的行[重复]

Question

我找不到任何答案，但我认为这很容易做到。

我有这个data.table：

DT = expand.grid(Season = c("Winter","Spring","Summer","Fall"),
                 Station = c("A","B","C"),
                 Group = c("1","2","3","4"))
DT$Value = seq(1,length(DT[,1]),1)
DT = data.table(DT)

我想根据这个其他data.table获取DT的一个子集：

indexTable = data.table(Season = c("Winter","Spring","Spring"),
                        Station = c("B","B","A"),
                        Group = c("1","2","3"))

基本上我只想要indexTable 中包含的DT 行。预期的结果是这个表：

expectedTable = data.table(Season = c("Winter","Spring","Spring"),
                           Station = c("B","B","A"),
                           Group = c("1","2","3"),
                           Value = c(5,18,26))

我正在尝试使用以下代码获取：

tryTable = DT[DT$Station %in% indexTable$Station &
              DT$Season %in% indexTable$Season &
              DT$Group %in% indexTable$Group,]

这不仅给了我我想要的 3 行，还给了我其他行 DT。

我做错了什么？有没有一种简单的方法可以使用 data.table 索引表示法获得expectedTable（例如使用setkey？）

Answer 1

您正在执行两个表的 INNER JOIN。

DT[
    indexTable
    , on = c("Season", "Station", "Group")
    , nomatch = 0
]

   Season Station Group Value
1: Winter       B     1     5
2: Spring       B     2    18
3: Spring       A     3    26

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参考

• JOINing data in R using data.table