给每个id相同的列值R

Question

我想给first.date基于first.date的水果=='苹果'每个唯一的ID相同的列值。

这是我有：

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 

这是我的灾难性的尝试：

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

预先感谢您

重复性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

目前还不清楚你想要当有对first.date和apple（给定名称）重复的条目做什么，这将只取前一个：

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