在R中使用data.table选择重复组的最近行数

Question

我有一个包含重复记录的数据集，可以由组确定。我想在最早的记录之后（按日期）将任何东西标记为重复（或者如果日期相同，则为第一行.id）。

library(data.table) 
library(lubridate) 

groupA <- c("A","B","C","A","B","C","D","E","A") 
groupB <- c("y","n","n","y","y","n","y","n","y") 
#ymd format 
date <- c("2017-04-01","2017-02-01","2017-03-01","2017-01-01","2017-05-01","2017-03-01","2017-07-01","2017-08-01","2017-09-01") 

mydata <- data.table(groupA, groupB, date=ymd(date)) 
check.dups <- mydata[,.("count"=.N),by=.(groupA,groupB)] 
#These are the duplicate keys 
check.dups <- check.dups[count>1,] 

#Create dupliate.flag on most recent example for duplicates 
keycols <- c("groupA","groupB") 
setkeyv(mydata, keycols) 
setkeyv(check.dups, keycols) 

我坚持对选择行逻辑创造重复标志的最早日期/第一row.id后。

#Select rows for duplicate flag 
mydata[check.dups,][date > min(date),dup.flag := ] 

任何帮助非常感谢。

预期输出：

一个标志由于日期，C标记因为row.id的（日期相同）

groupA groupB date  dup.flag 
A  y  2017-04-01 y 
B  n  2017-02-01 NA 
C  n  2017-03-01 NA 
A  y  2017-01-01 NA 
B  y  2017-05-01 NA 
C  n  2017-03-01 y 
D  y  2017-07-01 NA 
E  n  2017-08-01 NA 
A  y  2017-09-01 y 

Answer 1

请，尝试从data.table包duplicated()功能：

setkey(mydata, groupA, groupB, date) 
mydata[, dup := duplicated(mydata, by = c("groupA", "groupB"))] 

mydata 
# groupA groupB  date dup 
#1:  A  y 2017-01-01 FALSE 
#2:  A  y 2017-04-01 TRUE 
#3:  A  y 2017-09-01 TRUE 
#4:  B  n 2017-02-01 FALSE 
#5:  B  y 2017-05-01 FALSE 
#6:  C  n 2017-03-01 FALSE 
#7:  C  n 2017-03-01 TRUE 
#8:  D  y 2017-07-01 FALSE 
#9:  E  n 2017-08-01 FALSE