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[英]In R using data.table, how does one subset or query when the criteria field is an integer?
[英]In R using data.table, how does one exclude rows and how does one include NA values in an integer column
我经常使用data.table。 它运行良好,但我发现转换语法要花很长时间,因此它利用了二进制搜索的优势。
在下面的数据表中,如何1选择所有行,包括CPT值为NA
行,但排除CPT值为23456或10000的行。
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)
以下几行有效,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)。 有没有一种方法可以通过二进制方法删除行?
cpt.desc[!cpt %in% c(23456,10000),]
只是部分答案,因为我是data.table的新手。 自联接适用于数字,但字符串适用相同。 我确信其中一位专业数据表员知道该怎么做。
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)
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