I use superstore data and show how to extract date parts separately.
> head(superstore$Order.Date,5)
[1] "11-11-2014" "05-02-2014" "17-10-2014" "28-01-2014" "05-11-2014"
> day = strsplit(superstore$Order.Date,split = "-")
> head(day,5)
[[1]]
[1] "11" "11" "2014"
[[2]]
[1] "05" "02" "2014"
[[3]]
[1] "17" "10" "2014"
[[4]]
[1] "28" "01" "2014"
[[5]]
[1] "05" "11" "2014"