给每个 id 相同的列值 R

Question

我想根据水果=='apple' 的 first.date 为每个唯一 ID 赋予 first.date 相同的列值。

这就是我所拥有的：

 names      dates  fruit first.date
1   john 2010-07-01   kiwi       <NA>
2   john 2010-09-01  apple 2010-09-01
3   john 2010-11-01 banana       <NA>
4   john 2010-12-01 orange       <NA>
5   john 2011-01-01  apple 2010-09-01
6   mary 2010-05-01 orange       <NA>
7   mary 2010-07-01  apple 2010-07-01
8   mary 2010-07-01 orange       <NA>
9   mary 2010-09-01  apple 2010-07-01
10  mary 2010-11-01  apple 2010-07-01

这就是我想要的：

 names      dates  fruit first.date
1   john 2010-07-01   kiwi 2010-09-01
2   john 2010-09-01  apple 2010-09-01
3   john 2010-11-01 banana 2010-09-01
4   john 2010-12-01 orange 2010-09-01
5   john 2011-01-01  apple 2010-09-01
6   mary 2010-05-01 orange 2010-07-01
7   mary 2010-07-01  apple 2010-07-01
8   mary 2010-07-01 orange 2010-07-01
9   mary 2010-09-01  apple 2010-07-01
10  mary 2010-11-01  apple 2010-07-01

这是我的灾难性尝试：

getdates$first.date[is.na]<-getdates[getdates$first.date & getdates$fruit=='apple',]

提前谢谢你

可重现的 DF

names<-as.character(c("john", "john", "john", "john", "john", "mary", "mary","mary","mary","mary"))
dates<-as.Date(c("2010-07-01",  "2010-09-01", "2010-11-01", "2010-12-01", "2011-01-01", "2010-05-01", "2010-07-01", "2010-07-01",  "2010-09-01",  "2010-11-01"))
fruit<-as.character(c("kiwi","apple","banana","orange","apple","orange","apple","orange", "apple", "apple")) 
first.date<-as.Date(c(NA, "2010-09-01",NA,NA, "2010-09-01", NA, "2010-07-01", NA, "2010-07-01","2010-07-01"))
getdates<-data.frame(names,dates,fruit, first.date)

Answer 1

当first.date 和apple（对于给定名称）有重复条目时，不清楚您要做什么，这将只取第一个：

library(data.table)
dt = data.table(getdates)

dt[, first.date := first.date[fruit == 'apple'][1], by = names]
dt
#    names      dates  fruit first.date
# 1:  john 2010-07-01   kiwi 2010-09-01
# 2:  john 2010-09-01  apple 2010-09-01
# 3:  john 2010-11-01 banana 2010-09-01
# 4:  john 2010-12-01 orange 2010-09-01
# 5:  john 2011-01-01  apple 2010-09-01
# 6:  mary 2010-05-01 orange 2010-07-01
# 7:  mary 2010-07-01  apple 2010-07-01
# 8:  mary 2010-07-01 orange 2010-07-01
# 9:  mary 2010-09-01  apple 2010-07-01
#10:  mary 2010-11-01  apple 2010-07-01