Question

是否可以使用data.tables依次链接多个合并操作？

该功能类似于在ata.frames管道中连接多个d dplyr，但将其用于data.tables的方式类似于在两个data.tables中合并两个data.table下面的内容，然后根据需要操作data.table。但是只有您才能合并另一个library(dplyr) library(data.table) # data.frame df1 = data.frame(food = c("apples", "bananas", "carrots", "dates"), quantity = c(1:4)) df2 = data.frame(food = c("apples", "bananas", "carrots", "dates"), status = c("good", "bad", "rotten", "raw")) df3 = data.frame(food = c("apples", "bananas", "carrots", "dates"), rank = c("okay", "good", "better", "best")) df4 = left_join(df1, df2, by = "food") %>% mutate(new_col = NA) %>% # this is just to hold a position of mutation in the data.frame left_join(., df3, by = "food") # data.table dt1 = data.table(food = c("apples", "bananas", "carrots", "dates"), quantity = c(1:4)) dt2 = data.table(food = c("apples", "bananas", "carrots", "dates"), status = c("good", "bad", "rotten", "raw")) dt3 = data.table(food = c("apples", "bananas", "carrots", "dates"), rank = c("okay", "good", "better", "best")) # this is what I am not sure how to implement dt4 = merge(dt1, dt2, by = "food")[ food == "apples"](merge(dt4))。我承认this SO question here可能非常相似，也就是@ chinsoon12发表评论之后。

感谢您的帮助！

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Answer 1

可以链接带有on参数的多个data.table连接。请注意，如果j中没有更新运算符（“：=”），这将是一个右连接，但是如果使用“：=”（即添加列），则将成为左外部连接。有用的左侧帖子在这里Left join using data.table上加入。

使用上面的示例数据并在联接之间设置一个子集的示例：

dt4 <- dt1[dt2, on="food", `:=`(status = i.status)][
            food == "apples"][dt3, on="food", rank := i.rank]

##> dt4
## food quantity status rank
##1: apples        1   good okay

在联接之间添加新列的示例

dt4 <- dt1[dt2, on="food", `:=`(status = i.status)][
            , new_col := NA][dt3, on="food", rank := i.rank]

##> dt4
##      food quantity status new_col   rank
##1:  apples        1   good      NA   okay
##2: bananas        2    bad      NA   good
##3: carrots        3 rotten      NA better
##4:   dates        4    raw      NA   best

使用merge和magrittr管道的示例：

dt4 <-  merge(dt1, dt2, by = "food") %>%
           set( , "new_col", NA) %>% 
             merge(dt3, by = "food")

##> dt4
##      food quantity status new_col   rank
##1:  apples        1   good      NA   okay
##2: bananas        2    bad      NA   good
##3: carrots        3 rotten      NA better
##4:   dates        4    raw      NA   best

与data.tables链接多个data.table :: merge操作

1 个答案: