R package constructing time objects from date and hour(integer) - r

Question

I have data provided in the form of a date telling the day (format "YYYY-MM-DD", e.g. "2015-03-11" and the hours of the day numbered (0-23).
What is the most convenient way to produce time objects of the form
"2015-03-11" and hour = 0 -> "2015-03-11 00:00"
"2015-03-11" and hour = 1 -> "2015-03-11 01:00"
"2015-03-11" and hour = 2 -> "2015-03-11 02:00"
I could use the Date function from Base or something from xts or timeDate.
Should be easy but I am sure someone out there knows it quickly.
EDIT: the data is provided in 2 columns, one for the date and one numerical.

Answer 1

You don't need an external package to do that.
If your data is in this format:
df=data.frame(date=c("2015-03-11","2015-03-11","2015-03-11"),hour=0:2)
just apply the following function:
format(as.POSIXct(df$date)+df$hour*60*60, format = "%Y-%m-%d %H:%M")

Answer 2

Suppose we have this input:
date <- c("2015-03-11", "2015-03-12")
hour <- 2:3
then try one of these:
1) chron
library(chron)
as.chron(date) + hour/24
giving:
[1] (03/11/15 02:00:00) (03/12/15 03:00:00)
2) POSIXct. This one only uses the base of R, no packages:
as.POSIXct(date) + 3600 * hour
giving, on my system:
[1] "2015-03-11 02:00:00 EDT" "2015-03-12 03:00:00 EDT"
If you wanted the result in the UTC time zone use:
as.POSIXct(date, tz = "UTC") + 3600 * hour
3) lubridate
library(lubridate)
ymd(date) + hours(hour)
giving:
[1] "2015-03-11 02:00:00 UTC" "2015-03-12 03:00:00 UTC"
If you want it in the current time zone then:
ymd(date, tz = "") + hours(hour)
Note that the chron solution gives a date/time class that does not use time zones eliminating the many problems that time zones can cause. The POSIXct and lubridate solutions give the date/time in a specific time zone as shown.

Answer 3

You could try
dtime <- with(df, as.POSIXct(sprintf('%s %02d', date, hour),
format = "%Y-%m-%d %H"))
and then use format as in the other posts
Or
library(lubridate)
ymd_h(with(df, sprintf('%s %02d', date, hour)))
Or slightly more compact
ymd_h(do.call(paste, df))

Answer 4

Try this. You can format it without seconds afterwards using format if you wish, though I think it is preferable to keep it in POSIXct class so you can manipulate it afterwords (adding removing days, seconds, etc.)
as.POSIXct(do.call(paste, df), format = "%Y-%m-%d %H")
## [1] "2015-03-11 00:00:00 IST" "2015-03-11 01:00:00 IST" "2015-03-11 02:00:00 IST"
Though, If you insist on your exact output, here's the solution with format
format(as.POSIXct(do.call(paste, df), format = "%Y-%m-%d %H"), "%Y-%m-%d %H:%M")
## [1] "2015-03-11 00:00" "2015-03-11 01:00" "2015-03-11 02:00"
Data
df <- structure(list(V1 = structure(c(1L, 1L, 1L), .Label = "2015-03-11", class = "factor"),
V2 = 0:2), .Names = c("V1", "V2"), class = "data.frame", row.names = c(NA,
-3L))