ifelse Statement Returning Number Instead Of Date - r

Question

I have a series of dates in my code that are in an ifelse statement, that are returning a single numerical value instead of a date.
osa <- read.delim("C:/RMathew/RScripts/osaevents/osaevents.txt", stringsAsFactors=TRUE)
#
osa$datetime <- ymd_hms(osa$datetime)
osa$date <- as.Date(osa$datetime)
sixoclock <- 6*60*60
osa$daystart <- ymd_hms(ymd(osa$date) + sixoclock)
osa$dateplus <- osa$date + 1
osa$dateminus <- osa$date - 1
osa$dayend <- ymd_hms(ymd(osa$dateplus) + sixoclock)
osa$dateloca <- osa$datetime >= osa$daystart
osa$datelocb <- osa$datetime < osa$dayend
osa$milldate <- ifelse(osa$dateloca==TRUE & osa$datelocb==TRUE,
osa$date,osa$dateminus)
The place where this data originates considers the time between 6 AM on any given day to 6 AM the following day, as one day. The code above is trying to compare the date to the question of is it after 6 AM on a particular day, but before 6 AM on the following day, to assign it the earlier day's date (for whatever day it might be).
So far so good, but it returns a single number for the osa$milldate instead of the dates in the ifelse columns.
'data.frame': 897 obs. of 16 variables:
$ datetime : POSIXct, format: "2015-08-13 15:11:53" "2015-08-13 14:53:26" "2015-08-13 14:34:58" "2015-08-13 14:16:18" ...
$ stream : Factor w/ 1 level "fc": 1 1 1 1 1 1 1 1 1 1 ...
$ fe : num 18.1 18 17.6 18.1 18.5 ...
$ ni : num 2.97 2.99 2.92 3.2 3.32 ...
$ cu : num 3.41 3.35 2.99 3.58 3.73 ...
$ pd : num 138 157 139 166 183 ...
$ mg : num 13.8 13.8 14.4 14.3 13.9 ...
$ so : num 9.67 9.81 9.65 10.58 11.37 ...
$ date : Date, format: "2015-08-13" "2015-08-13" "2015-08-13" "2015-08-13" ...
$ daystart : POSIXct, format: "2015-08-13 06:00:00" "2015-08-13 06:00:00" "2015-08-13 06:00:00" "2015-08-13 06:00:00" ...
$ dateplus : Date, format: "2015-08-14" "2015-08-14" "2015-08-14" "2015-08-14" ...
$ dateminus: Date, format: "2015-08-12" "2015-08-12" "2015-08-12" "2015-08-12" ...
$ dayend : POSIXct, format: "2015-08-14 06:00:00" "2015-08-14 06:00:00" "2015-08-14 06:00:00" "2015-08-14 06:00:00" ...
$ dateloca : logi TRUE TRUE TRUE TRUE TRUE TRUE ...
$ datelocb : logi TRUE TRUE TRUE TRUE TRUE TRUE ...
$ milldate : num 16660 16660 16660 16660 16660 ...
Thoughts? Also, there is likely to be a more elegant way to do this.

Answer 1

See the help file for ifelse
Warning:
The mode of the result may depend on the value of ‘test’ (see the
examples), and the class attribute (see ‘oldClass’) of the result
is taken from ‘test’ and may be inappropriate for the values
selected from ‘yes’ and ‘no’.
Sometimes it is better to use a construction such as
(tmp <- yes; tmp[!test] <- no[!test]; tmp)
, possibly extended to handle missing values in ‘test’.
This describes precisely what is going on in your example -- the date class attribute is lost -- and a work around -- a multi-step approach.
osa$milldate <- osa$date
ind<- osa$dateloca==TRUE & osa$datelocb==TRUE
osa$milldate[!ind] <- osa$dateminus
Another option is replace.

Answer 2

A. Webb set me on the right path. The ifelse class was stripping the answer of the date format. The solution above with the index seemed to jumble the date order for some reason. As A. Webb pointed out, in the help file, the following line fixed it immediately.
class(osa$milldate) <- class(osa$date)