Loop does not work: Error in else statement

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Frank S.
Sent: Monday, September 29, 2014 9:17 PM
To: r-help at r-project.org
Subject: [R] Loop does not work: Error in else statement

Hi to all members of R list,



I m working with data.table package, and with 6
variables: "ID" (Identifier), "born" (Birthdate), "start" (Starting
date), "register" (date of measurement), "value"and "end" (date of
expiration). So, the natural order of dates would be: born =< start =<
register =< end.  As an example, I have: DT <- data.table(ID =
as.factor(rep(1:4,each=2)),

     born =
as.Date(rep(c("1955-02-20", "1990-07-25", "1972-03-18", "1988-05-
03"),each=2)),

     start =
as.Date(rep(c("1953-03-28", "1990-07-01", "1983-09-05", "1988-07-
18"),each=2)),

     register =
as.Date(c("1955-08-11", "1958-03-28",
"1990-07-09", "1992-07-01",

                "1983-09-05",
"2002-09-28", "1992-07-10", "1993-03-12")),

     value =
c(205, 346, 34, 76, 320, 148, 209, 274),

     end =
as.Date(rep(c("1960-11-05", "1997-10-15", "2002-09-27", "1997-03-
02"),each=2)))



I would want to make 3 operations:1. First: Remove entire ID s where
"start" is previous to "born" date (excepting those subjects whose
month and year values are the same in "start" and "born" variables: I
assign "born"
date to "start" date in these cases).Afterwords:2. Remove only specific
rows (not all ID) where  register  is previous to  start .3.Remove only
specific rows (not all ID) where  end  is previous to  register .

I have: DT[ , {    if (all(born > start))       {     indx <-
which(paste(year(born)) == paste(year(start)) &  paste(month(born)) ==
paste(month(start)))      result <- list(born=born[indx],
start=born[indx], register=register[indx], value=value[indx],
end=end[indx])      }        if (all(register > start) | all(end >
register))         {         indx <- which((register > start) | (end >
register))         result <- list(born=born[indx], start=start[indx],
register=register[indx], value=value[indx], end=end[indx])          }
else         {         NULL         }   else     {     indx <-
which(all(register > start) | all(end > register))     result <-
list(born=born[indx], start=start[indx], register=register[indx],
value=value[indx], end=end[indx])      }   result   }, by=ID] BUT I GET
AN ERROR MESSAGE: Error: syntax error, unexpected ELSE in "else"
Please, can anyone help me? Thank you!!