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 key 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,在这种情况下,我可以手动设置它:
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"
问题:
这是通缉的行为,还是一个错误?
选择:
使用
merge
语法可以达到我的期望: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"
用法:添加一列:
如果我想将
abn
列从dtab
合并到dtp
,则有一种简便的方法可以编写dtab[dtp]
来松开键和列的顺序: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
示例它如何工作
如果
dtab
中还有其他列,但仅abn
应该合并,则还有另一种可能性(我的最爱):##### 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
或分配它:
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), key 将保留下来。
@ 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
最佳答案
# v1.9.5+
key(dtp[dtab])
# [1] "pid" "year"
关于r - [.data.table(merge-X [Y])键在v.1.9.3版中丢失了,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/23338726/