When I read in your data, I get the following since I am in the EDT time
zone:

> df<-structure(list(date = structure(c(1395874800, 1395874800, 1395874800,
+ 1395874800, 1395874800), class = c("POSIXct", "POSIXt"), tzone = ""),
+      hour = structure(c(-2209121804, -2209121567, -2209121005,
+      -2209118616, -2209116160), class = c("POSIXct", "POSIXt"), tzone =
""),
+      s.100 = c(29L, 36L, 6L, 53L, 18L)), .Names = c("date", "hour",
+ "s.100"), row.names = c(NA, -5L), class = "data.frame")
>
> df
                 date                hour s.100
1 2014-03-26 19:00:00 1899-12-30 06:03:16    29
2 2014-03-26 19:00:00 1899-12-30 06:07:13    36
3 2014-03-26 19:00:00 1899-12-30 06:16:35     6
4 2014-03-26 19:00:00 1899-12-30 06:56:24    53
5 2014-03-26 19:00:00 1899-12-30 07:37:20    18


I assume your real date is probably 2014-03-27 if it supposed to be GMT.
 And your 'hour' is funny for probably the same reason.  You can easily
convert the hundredth of a second in the original input.

Now I would really like to ask how you got to this point.  Did you
originally read in and convert the data yourself, or is this a source that
you do not have any control over?  If the former, then just use the correct
conversion.  As shown below, if you have hundredths of a second, that will
be converted correctly and you don't need the extra column.

> x <- as.POSIXct("2014-04-29 12:00:00.345")  # decimal seconds that are
converted
>
> x
[1] "2014-04-29 12:00:00 EDT"
> format(x, format = "%H:%M:%OS3")  # print with 3 decimals
[1] "12:00:00.345"

If you have the choice, start over again and do it correctly.  If not,
convert the various components to the correct character format for your
timezone, combine back together and then use the conversion shown above.


Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.


On Tue, Apr 29, 2014 at 9:06 AM, Massimo Bressan <mbressan@arpa.veneto.it>wrote:

> I have this dataframe:
>
> df<-structure(list(date = structure(c(1395874800, 1395874800, 1395874800,
> 1395874800, 1395874800), class = c("POSIXct", "POSIXt"), tzone = ""),
>      hour = structure(c(-2209121804, -2209121567, -2209121005,
>      -2209118616, -2209116160), class = c("POSIXct", "POSIXt"), tzone =
> ""),
>      s.100 = c(29L, 36L, 6L, 53L, 18L)), .Names = c("date", "hour",
> "s.100"), row.names = c(NA, -5L), class = "data.frame")
>
>
> and I would like to sum first two columns ("date" and "hour") so that to
> end up with a new column, say "date_hour", storing both the information
> about the "date" and the "hour" in one POSIXct object;
>
> I have been reading that POSIXct objects are a measure of seconds from a
> given origin (1st Jan 1970), so that a possible solution is to tranform the
> column "hour" into seconds and then add it to the column "date";
>
> but, is there a staightforward solution for accomplishing this task?
> I've been trying to extract from the column "hour" the digits representing
> hours, minutes and seconds and transform everything into seconds but that
> seem to me quite cumbersome approach...
>
> and finally, one more question: is it possible to represent hundred of
> seconds as given in the column "s.100" of the given dataframe within the
> same new POSIXct object "date_hour"?
>
>
> thanksfor the support
>
>
>
>
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>
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