Updating Variable using functions in data.table?

Question

This is a very quick question, I also asked a more complicated one in this link

In this link, Roland kindly gave a very elegant solution to my problems. But I want to figure out why my solution doesn't work.

DT <- data.table(UID = paste0("UID",rep(1:5,each=2), 
  date = as.IDate("2012-01-01","2012-01-02","2012-01-03","2012-01-04","2012-01-05","2012-01-06","2012-02-01","2012-02-02","2012-02-03","2012-02-04"),
  value = c(1:10)))

This is the fake data set.

Now I want to create a new variable called Val2 based on the following condition:

** Whether the date of each row is no "2012-01-02","2012-02-02".

To achieve this, I tried this

1.  f <- function(x){ 
test <- ifelse(x %in% as.Date(c("2012-01-02","2012-02-02")) , TRUE, FALSE)
return(test)
}

DT[,Val2:= f(date)]

But all Val2 are true, which is obviously wrong.

As Roland pointed in my previous problem, I tried another one.

DT[, Val2:= sapply(date, function(x) x %in% as.Date(c("2012-01-02","2012-02-02")))]

Still not working with the following error:

Error in as.Date.default(x, ...) : do not know how to convert 'x' to class ate?

Also I tried to modified based on the error hints, but all failed.

Could you offer some suggestions? Thanks!

I beg to differ. Paste from the question into your R interpreter. — Matthew Lundberg
– Matthew Lundberg, Commented Jan 16, 2014 at 2:56
@MatthewLundberg I just copied the code from Rstudio, but when I copied back it doesn't work neither..Now hope the code is OK. Thanks — Bigchao
– Bigchao, Commented Jan 16, 2014 at 3:08

Matthew Lundberg · Accepted Answer · 2014-01-16 03:00:39Z

Compare to an object of the same class (IDate). You also do not need to use ifelse to here, as it is just returning the value of %in%.

DT[,val2 := date %in% as.IDate(c("2012-01-02","2012-02-02"))]
> DT
     UID       date value  val2
 1: UID1 2012-01-01     1 FALSE
 2: UID1 2012-01-02     2  TRUE
 3: UID2 2012-01-03     3 FALSE
 4: UID2 2012-01-04     4 FALSE
 5: UID3 2012-01-05     5 FALSE
 6: UID3 2012-01-06     6 FALSE
 7: UID4 2012-02-01     7 FALSE
 8: UID4 2012-02-02     8  TRUE
 9: UID5 2012-02-03     9 FALSE
10: UID5 2012-02-04    10 FALSE

DT, prior to the addition of val2:

structure(list(UID = c("UID1", "UID1", "UID2", "UID2", "UID3", 
"UID3", "UID4", "UID4", "UID5", "UID5"), date = structure(c(15340L, 
15341L, 15342L, 15343L, 15344L, 15345L, 15371L, 15372L, 15373L, 
15374L), class = c("IDate", "Date")), value = 1:10), .Names = c("UID", 
"date", "value"), row.names = c(NA, -10L), class = c("data.table", 
"data.frame"))

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