Dates are not keeping specified format in R data frame - r

Question

Simply put, I'm grabbing dates for events that meet certain conditions in df1 and putting them in a new data frame (df2). The formatting of dates in df2 should be the same formatting in df1 ("2000-09-12", or %Y-%m-%d). However, the dates in df2 read "11212", "11213", etc.
to generate data:
"Date"<-c("2000-09-08", "2000-09-11","2000-09-12","2000-09-13","2000-09-14","2000-09-15","2000-09-18","2000-09-19","2000-09-20","2000-09-21", "2000-09-22","2000-09-25")
"Event"<-c("A","N","O","O","O","O","N","N","N","N","N","A")
df1<-data.frame(Date,Event)
df1
Date Event
1 2000-09-08 A
2 2000-09-11 N
3 2000-09-12 O
4 2000-09-13 O
5 2000-09-14 O
6 2000-09-15 O
7 2000-09-18 N
8 2000-09-19 N
9 2000-09-20 N
10 2000-09-21 N
11 2000-09-22 N
12 2000-09-25 A
here is the code:
"df2"<-data.frame()
"tmp"<-data.frame(1,2)
i<-c(1:4)
for (x in i)
{
date1<- df1$Date[df1$Event=="O"][x]
date2<- df1$Date[df1$Event=="A" & df1$Date => date1] [1]
as.numeric(difftime(date2, date1))->tmp[1,2]
as.Date(as.character(df1$Date[df1$Event=="O"][x]), "%Y-%m-%d")->tmp[1,1] ##the culprit
rbind(df2, tmp)->df2
}
Loop output looks like this:
X1 X2
1 11212 13
2 11213 12
3 11214 11
4 11215 10
I want it to look like this:
X1 X2
1 "2000-09-12" 13
2 "2000-09-13" 12
3 "2000-09-14" 11
4 "2000-09-14" 10

Answer 1

If I understand correctly, the OP wants to find for each "O" event the difference in days to the next following "A" event.
This can be solved using a rolling join. We extract the "O" events and the "A" events into two separate data.tables and join both on date.
This will avoid all the hassle with the data format and works also if df1 is not already ordered by Date.
library(data.table)
setDT(df1)[Event == "A"][df1[Event == "O"],
on = "Date", roll = -Inf, .(Date, x.Date - i.Date)]
Date V2
1: 2000-09-12 13 days
2: 2000-09-13 12 days
3: 2000-09-14 11 days
4: 2000-09-15 10 days
Note that roll = -Inf rolls backwards (next observation carried backward (NOCB)) because the date of the next "A" event is required.
Data
Date <- as.Date(c("2000-09-08", "2000-09-11","2000-09-12","2000-09-13","2000-09-14","2000-09-15",
"2000-09-18","2000-09-19","2000-09-20","2000-09-21", "2000-09-22","2000-09-25"))
Event <- c("A","N","O","O","O","O","N","N","N","N","N","A")
df1 <- data.frame(Date,Event)