在使用data.table的R中，如何排除行，如何在整数列中包含NA值

Question

我使用的data.table相当多。它工作的很好，但我发现它花了很长时间来转换我的语法，以便利用二进制搜索。

在下面的数据表会怎么选择1所有行，包括在CPT值是NA但不包括行，其中的CPT值是23456或10000

cpt <- c(23456,23456,10000,44555,44555,NA) 
description <- c("tonsillectomy","tonsillectomy in >12 year old","brain transplant","castration","orchidectomy","miscellaneous procedure") 
cpt.desc <- data.table(cpt,description) 

setkey(cpt.desc,cpt) 

下面这行工作，但我认为，它使用矢量扫描方法而不是二进制搜索（或二进制排除）。有没有办法通过二进制方法删除行？

cpt.desc[!cpt %in% c(23456,10000),] 

Answer 1

只有部分答案，因为我是新来的data.table。自连接适用于数字，但字符串也一样。我确信其中一个专业数据表会知道该怎么做。

library(data.table) 

n <- 1000000 
cpt.desc <- data.table(
    cpt=rep(c(23456,23456,10000,44555,44555,NA),n), 
    description=rep(c("tonsillectomy","tonsillectomy in >12 year old","brain transplant","castration","orchidectomy","miscellaneous procedure"),n)) 

# Added on revision. Not very elegant, though. Faster by factor of 3 
# but probably better scaling 
setkey(cpt.desc,cpt) 
system.time(a<-cpt.desc[-cpt.desc[J(23456,45555),which=TRUE]]) 
system.time(b<-cpt.desc[!(cpt %in% c(23456,45555))]) 
str(a) 
str(b) 

identical(as.data.frame(a),as.data.frame(b)) 

# A self-join works Ok with numbers 
setkey(cpt.desc,cpt) 
system.time(a<-cpt.desc[cpt %in% c(23456,45555),]) 
system.time(b<-cpt.desc[J(23456,45555)]) 
str(a) 
str(b) 

identical(as.data.frame(a),as.data.frame(b)[,-3]) 

# But the same failes with characters 
setkey(cpt.desc,description) 
system.time(a<-cpt.desc[description %in% c("castration","orchidectomy"),]) 
system.time(b<-cpt.desc[J("castration","orchidectomy"),]) 
identical(as.data.frame(a),as.data.frame(b)[,-3]) 

str(a) 
str(b)