select R 中具有 data.table 的重复组的最新行

Question

我有一个包含重复记录的数据集，可以由一组来确定。我想将最早记录（按日期）之后的所有内容标记为重复项（如果日期相同，则为第一个 row.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)

我坚持在最早 date/first row.id 之后选择行的逻辑来创建重复标志。

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

非常感谢任何帮助。

预期输出：

A 标记是由于日期，C 标记是因为 row.id（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 data.table 包中的 duplicated() 函数：

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

select R 中具有 data.table 的重复组的最新行

select most recent rows for duplicate groups with data.table in R

r

lubridate

data.table