我有2个data.tables dtp和dtab。
require(data.table)
set.seed(1)
dtp <- data.table(pid = gl(3, 3, labels = c("du", "i", "nouana")),
year = gl(3, 1, 9, labels = c("2007", "2010", "2012")),
val = rnorm(9), key = c("pid", "year"))
dtab <- data.table(pid = factor(c("i", "nouana")),
year = factor(c("2010", "2000")),
abn = sample(1:5, 2, replace = TRUE), key =
c("pid", "year"))
dtp
## pid year val
## 1: du 2007 -0.6264538
## 2: du 2010 0.1836433
## 3: du 2012 -0.8356286
## 4: i 2007 1.5952808
## 5: i 2010 0.3295078
## 6: i 2012 -0.8204684
## 7: nouana 2007 0.4874291
## 8: nouana 2010 0.7383247
## 9: nouana 2012 0.5757814
dtab
## pid year abn
## 1: i 2010 2
## 2: nouana 2000 4
如果我使用[.data.table合并它们，则密钥会丢失：
dtp[dtab]
## pid year val abn
## 1: i 2010 0.3295078 2
## 2: nouana 2000 NA 4
key(dtp[dtab]) # key got lost
## NULL # v.1.9.3
##### which was in 1.8.10
## [1] "pid" "year"
好的，对于这种情况，我可以手动设置：
res1 <- setkeyv(dtp[dtab], key(dtp))
res1
## pid year val abn
## 1: i 2010 0.3295078 2
## 2: nouana 2000 NA 4
key(res1) # repaired it
## [1] "pid" "year"
这是想要的行为，还是一个错误？
使用merge语法完成了我的预期：
merge(dtp, dtab, all.y = TRUE)
## pid year val abn
## 1: i 2010 0.3295078 2
## 2: nouana 2000 NA 4
key(merge(dtp, dtab, all.y = TRUE)) # everything ok
## [1] "pid" "year"
如果我想将abn列dtab合并到dtp，可以轻松编写dtab[dtp]丢失密钥和列的顺序：< / p>
dtab[dtp]
## pid year abn val
## 1: du 2007 NA -0.6264538
## 2: du 2010 NA 0.1836433
## 3: du 2012 NA -0.8356286
## 4: i 2007 NA 1.5952808
## 5: i 2010 2 0.3295078
## 6: i 2012 NA -0.8204684
## 7: nouana 2007 NA 0.4874291
## 8: nouana 2010 NA 0.7383247
## 9: nouana 2012 NA 0.5757814
如果dtab中有其他cols，但只有abn应该合并，还有另一种可能性（我最喜欢的）：
##### just show it:
## dtp[dtab[dtp, abn]] # v.1.8.10
dtp[dtab[dtp, abn, by = .EACHI]] # since v.1.9.3
## pid year val abn
## 1: du 2007 -0.6264538 NA
## 2: du 2010 0.1836433 NA
## 3: du 2012 -0.8356286 NA
## 4: i 2007 1.5952808 NA
## 5: i 2010 0.3295078 2
## 6: i 2012 -0.8204684 NA
## 7: nouana 2007 0.4874291 NA
## 8: nouana 2010 0.7383247 NA
## 9: nouana 2012 0.5757814 NA
或分配：
dtp[dtab[dtp], abn := abn] # assign it
dtp
## pid year val abn
## 1: du 2007 -0.6264538 NA
## 2: du 2010 0.1836433 NA
## 3: du 2012 -0.8356286 NA
## 4: i 2007 1.5952808 NA
## 5: i 2010 0.3295078 2
## 6: i 2012 -0.8204684 NA
## 7: nouana 2007 0.4874291 NA
## 8: nouana 2010 0.7383247 NA
## 9: nouana 2012 0.5757814 NA
key(dtp) # ok
## [1] "pid" "year"
在后一种情况下（显示或分配），密钥仍然存在。
@ Arun：这是sessionInfo()：
sessionInfo()
## R version 3.1.0 (2014-04-10)
## Platform: powerpc64-unknown-linux-gnu (64-bit)
## locale:
## [1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
## [3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
## [5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
## [7] LC_PAPER=en_US.UTF-8 LC_NAME=C
## [9] LC_ADDRESS=C LC_TELEPHONE=C
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
## attached base packages:
## [1] stats graphics grDevices utils datasets methods base
## other attached packages:
## [1] data.table_1.9.3
## loaded via a namespace (and not attached):
## [1] plyr_1.8 reshape2_1.2.2 stringr_0.6.2