[R] Extract time from irregular date and time data records

[Sam Albers]

Apologies. I was searching using the wrong search terms. This is
clearly a string issue. I've added the solution below.

Sam

On Tue, May 29, 2012 at 11:39 AM, Sam Albers <tonightsthenight at gmail.com> wrote:
> Hello,
>
> I am having a problem making use of some data outputted from an
> instrument in a somewhat weird format. The instrument outputs two
> columns - one called JulianDay.Hour and one called Minutes.Seconds. I
> would like to convert these columns into a single column with a time.
> So I was using substr() and paste to extract that info. This works
> fine for the JulianDay.Hour column as there are always five characters
> in an entry. However in the Minutes.Seconds column any leading zeroes
> are dropped by the instrument. So if I use substr() to selected based
> on character position I end up with incorrect times. So for example:
>
> ## df
>
> df<-structure(list(Temperature = c(18.63, 18.4, 18.18, 16.99, 16.86,
> 11.39, 11.39, 11.37, 11.37, 11.37, 11.37), JulianDay.Hour = c(22610L,
> 22610L, 22610L, 22610L, 22610L, 22611L, 22611L, 22611L, 22611L,
> 22611L, 22611L), Minutes.Seconds = c(4608L, 4611L, 4614L, 4638L,
> 4641L, 141L, 144L, 208L, 211L, 214L, 238L)), .Names = c("Temperature",
> "JulianDay.Hour", "Minutes.Seconds"), row.names = c(3176L, 3177L,
> 3178L, 3179L, 3180L, 3079L, 3080L, 3054L, 3055L, 3056L, 3057L
> ), class = "data.frame")
>
> ## Extraction method for times
> df$Time.Incorrect <- paste(substr(df$JulianDay.Hour, 4,5),":",
>                 substr(df$Minutes.Seconds,1,2),":",
>                 substr(df$Minutes.Seconds,3,4),
>                 sep="")
>
>
## Addition of leading zeroes

df$Time.Correct <- paste(substr(df$JulianDay.Hour, 4,5),":",
                           substr(formatC(df$Minutes.Seconds, width =
4, format = "d", flag = "0"),1,2),":",
                           substr(formatC(df$Minutes.Seconds, width =
4, format = "d", flag = "0"),3,4),
                           sep="")

>
>
> ## Note the absence of leading zeroes in the Minutes.Seconds leading
> to incomplete time records (df$Time.Incorrect)
> df
>
> ##
>
> So can anyone recommend a good way to extract a time from variables
> like these two? Basically this is subsetting a string issue.
>
> Thanks in advance!
>
> Sam