r data.table 就地连接多列

data.table是惊人的。

我想进行就地联接，但保留两个表中的所有列。这个问题 https://stackoverflow.com/questions/34598139/left-join-using-data-table/34600831演示如何对单个列执行此操作。当我希望连接表中的所有列都出现在最终结果中并将其全部完成在一个内存位置时，如何概括这一点。

library(data.table)
dt1 <- data.table(col1 = c("a", "b", "c"), 
                  col2 = 1:3, 
                  col3 = c(TRUE, FALSE, FALSE))

setkey(dt1, col1)

set.seed(1)
dt2 <- data.table(col1 = sample(c("a", "b", "c"), size = 10, replace = TRUE), 
                  another_col = sample(1:10, size = 10, replace = TRUE), 
                  and_anouther = sample(c(TRUE, FALSE), size = 10, replace = TRUE))

setkey(dt2, col1)

# I want to stick the columns from dt1 onto dt2

# this works
dt3 <- dt2[dt1]
dt3
    col1 another_col and_anouther col2  col3
 1:    a           9        FALSE    1  TRUE
 2:    b           2        FALSE    2 FALSE
 3:    b           9        FALSE    2 FALSE
 4:    b           6        FALSE    2 FALSE
 5:    b           5         TRUE    2 FALSE
 6:    b           8        FALSE    2 FALSE
 7:    c           9         TRUE    3 FALSE
 8:    c           5        FALSE    3 FALSE
 9:    c           7        FALSE    3 FALSE
10:    c           6        FALSE    3 FALSE

# but i want to do this by reference

# this works for one column
dt2[dt1, col2 := i.col2]
dt2

    col1 another_col and_anouther col2
 1:    a           3        FALSE    1
 2:    a           8         TRUE    1
 3:    a           8         TRUE    1
 4:    b           2         TRUE    2
 5:    b           7        FALSE    2
 6:    b          10         TRUE    2
 7:    b           4        FALSE    2
 8:    c           4         TRUE    3
 9:    c           5         TRUE    3
10:    c           8         TRUE    3

# ok, remove that column
dt2[, col2 := NULL]

# now try to join multiple columns 
# this doesn't work
dt2[dt1, (col2 := i.col2, 
          col3 := i.col3)]

# neither does this
dt2[dt1, .(col2 := i.col2, 
          col3 := i.col3)]

# this just give me to the two columns
dt2[dt1, .(col2 = i.col2, 
           col3 = i.col3)]
dt2
   col2  col3
 1:    1  TRUE
 2:    1  TRUE
 3:    1  TRUE
 4:    2 FALSE
 5:    2 FALSE
 6:    2 FALSE
 7:    2 FALSE
 8:    3 FALSE
 9:    3 FALSE
10:    3 FALSE  

                ^

^{Created on 2018-10-30 by the reprex package https://reprex.tidyverse.org (v0.2.1)}

差不多，我想要结果dt3，但我希望它通过引用创建为dt2。谢谢！

我应该看看还有一个问题 https://stackoverflow.com/questions/30913338/join-two-data-tables-and-use-only-one-column-from-second-dt-in-r?rq=1与此相关的很棒的参考。 https://rawgit.com/wiki/Rdatatable/data.table/vignettes/datatable-reference-semantics.html。我所需要做的就是使用函数形式:=操作员。

dt2[dt1, `:=` (col2 = i.col2, 
          col3 = i.col3)]

dt2
    col1 another_col and_anouther col2  col3
 1:    a           3        FALSE    1  TRUE
 2:    a           8         TRUE    1  TRUE
 3:    a           8         TRUE    1  TRUE
 4:    b           2         TRUE    2 FALSE
 5:    b           7        FALSE    2 FALSE
 6:    b          10         TRUE    2 FALSE
 7:    b           4        FALSE    2 FALSE
 8:    c           4         TRUE    3 FALSE
 9:    c           5         TRUE    3 FALSE
10:    c           8         TRUE    3 FALSE