r - data.table 内/外连接与 NA 在双 bug 类型的连接列中？

Question

按照这篇维基百科文章 SQL join我想清楚地了解我们如何与 data.table 进行连接。
在这个过程中，我们可能在加入 NA 时发现了一个错误。
以维基为例:

R) X = data.table(name=c("Raf","Jon","Ste","Rob","Smi","Joh"),depID=c(31,33,33,34,34,NA),key="depID")
R) Y = data.table(depID=c(31,33,34,35),depName=c("Sal","Eng","Cle","Mar"),key="depID")
R) X
   name depID
1:  Joh    NA
2:  Raf    31
3:  Jon    33
4:  Ste    33
5:  Rob    34
6:  Smi    34
R) Y
   depID depName
1:    31     Sal
2:    33     Eng
3:    34     Cle
4:    35     Mar

左外连接

R) merge.data.frame(X,Y,all.x=TRUE)
  depID name depName
1    31  Raf     Sal
2    33  Jon     Eng
3    33  Ste     Eng
4    34  Rob     Cle
5    34  Smi     Cle
6    NA  Joh    <NA>

merge.data.table不要输出相同的结果并显示我认为是 lign 2 上的错误。

R) merge(X,Y,all.x=TRUE)
   depID name depName
1:    NA  Joh     Eng
2:    31  Raf      NA
3:    33  Jon     Eng
4:    33  Ste     Eng
5:    34  Rob     Cle
6:    34  Smi     Cle
R) Y[X] #same -> :(
   depID depName name
1:    NA     Eng  Joh
2:    31      NA  Raf
3:    33     Eng  Jon
4:    33     Eng  Ste
5:    34     Cle  Rob
6:    34     Cle  Smi

右外连接
看起来一样

R) merge.data.frame(X,Y,all.y=TRUE)
  depID name depName
1    31  Raf     Sal
2    33  Jon     Eng
3    33  Ste     Eng
4    34  Rob     Cle
5    34  Smi     Cle
6    35 <NA>     Mar

R) merge(X,Y,all.y=TRUE)
   depID name depName
1:    NA  Joh     Eng
2:    31   NA     Sal
3:    33  Jon     Eng
4:    33  Ste     Eng
5:    34  Rob     Cle 
6:    34  Smi     Cle
7:    35   NA     Mar

内(自然)连接

R) merge.data.frame(X,Y)
  depID name depName
1    31  Raf     Sal
2    33  Jon     Eng
3    33  Ste     Eng
4    34  Rob     Cle
5    34  Smi     Cle
R) merge(X,Y)
   depID name depName
1:    NA  Joh     Eng
2:    33  Jon     Eng
3:    33  Ste     Eng
4:    34  Rob     Cle
5:    34  Smi     Cle

Answer 1

是的，它看起来像是一个(令人尴尬的)与关键 NA 相关的新错误。还有其他关于 NA in key 不可能的讨论，但我没有意识到它会以这种方式搞砸。会调查。谢谢 ...

#2453 NA in double key column messes up joins (NA in integer and character ok)

现在在 1.8.7 (commit 780) 中修复，来自 NEWS :

NA in a join column of type double could cause both X[Y] and merge(X,Y) to return incorrect results, #2453. Due to an errant x==NA_REAL in the C source which should have been ISNA(x). Support for double in keyed joins is a relatively recent addition to data.table, but embarassing all the same. Fixed and tests added. Many thanks to statquant for the thorough and reproducible report.