Convert a date vector into Julian day in R - r

Question

I have a column of dates in the format:
16Jun10
and I would like to extract the Julian day.
I have various years.
I have tried the functions julian and mdy.date and it doesn't seem to work.

Answer 1

Try the following to convert from class character(i.e. text) to class POSIXlt, and then extract Julian day (yday):
tmp <- as.POSIXlt("16Jun10", format = "%d%b%y")
tmp$yday
# [1] 166
For more details on function settings:
?POSIXlt
?DateTimeClasses
Another option is to use a Date class, and then use format to extract a julian day (notice that this class define julian days between 1:366, while POSIXlt is 0:365):
tmp <- as.Date("16Jun10", format = "%d%b%y")
format(tmp, "%j")
# [1] "167"

Answer 2

Similarly:
require(lubridate)
x = as.Date('2010-06-10')
yday(x)
[1] 161
Also note, using lubridate:
> dmy('16Jun10')
[1] "2010-06-16 UTC"

Answer 3

You can use R's insol package which has a JD(x, inverse=FALSE) function which converts POSIXct to Julian Day Number (JDN).
insol package also has JDymd(year,month,day,hour=12,minute=0,sec=0) for custom dates.
To display the whole Julian Date (JD) you possibly have to set options(digits=16).

Answer 4

my.data = read.table(text = "
OBS MONTH1 DAY1 YEAR1
1 3 1 2012
2 3 31 2012
3 4 1 2012
4 4 30 2012
5 5 1 2012
6 5 31 2012
7 6 1 2012
8 6 30 2012
9 7 1 2012
10 7 31 2012
", header = TRUE, stringsAsFactors = FALSE)
my.data$MY.DATE1 <- do.call(paste, list(my.data$MONTH1, my.data$DAY1, my.data$YEAR1))
my.data$MY.DATE1 <- as.Date(my.data$MY.DATE1, format=c("%m %d %Y"))
my.data$my.julian.date <- as.numeric(format(my.data$MY.DATE1, "%j"))
my.data
Returns, which technically is incorrect since Julian dates do not return to 1 on the first day of each January:
http://en.wikipedia.org/wiki/Julian_day
The dates below are Ordinal dates:
OBS MONTH1 DAY1 YEAR1 MY.DATE1 my.julian.date
1 1 3 1 2012 2012-03-01 61
2 2 3 31 2012 2012-03-31 91
3 3 4 1 2012 2012-04-01 92
4 4 4 30 2012 2012-04-30 121
5 5 5 1 2012 2012-05-01 122
6 6 5 31 2012 2012-05-31 152
7 7 6 1 2012 2012-06-01 153
8 8 6 30 2012 2012-06-30 182
9 9 7 1 2012 2012-07-01 183
10 10 7 31 2012 2012-07-31 213

Answer 5

Here are my R versions of code originally written in APL and converted to J. We call this pseudo-Julian because it is only intended for dates after October 15, 1582 which is when calendar reform, in some parts of the Western world, arbitrarily changed the date.
#* toJulian: convert 3-element c(Y,M,D) timestamp into pseudo-Julian day number.
toJulian<- function(TS3)
{ mm<- TS3[2]
xx<- 0
if( mm<=2) {xx<- 1}
mm<- (12*xx)+mm
yy<- TS3[1]-xx
nc<- floor(0.01*yy)
jd<- floor(365.25*yy)+floor(30.6001*(1+mm))+TS3[3]+1720995+(2-(nc-floor(0.25*nc)))
return(jd)
#EG toJulian c(1959,5,24) -> 2436713
#EG toJulian c(1992,12,16) -> 2448973
}
Here's the inverse function:
#* toGregorian: convert pseudo-Julian day number to timestamp in form c(Y,M,D)
# (>15 Oct 1582). Adapted from "Numerical Recipes in C" by Press,
# Teukolsky, et al.
toGregorian<- function(jdn)
{ igreg<- 2299161 # Gregorian calendar conversion day c(1582,10,15).
ja<- floor(jdn)
xx<- 0
if(igreg<=ja){xx<- 1}
jalpha<- floor((floor((xx*ja)-1867216)-0.25)/36524.25)
ja<- ((1-xx)*ja) + ((xx*ja)+1+jalpha-floor(0.25*jalpha))
jb<- ja+1524
jc<- floor(6680+((jb-2439870)-122.1)/365.25)
jd<- floor(365.25*jc)
je<- floor((jb-jd)/30.6001)
id<- floor((jb-jd)-floor(30.6001*je))
mm<- floor(je-1)
if(12<mm){mm<- mm-12}
iyyy<- floor(jc-4715)
if(mm>2){iyyy<- iyyy-1}
if(0>iyyy){iyyy<- iyyy-1}
gd<- c(iyyy, mm, id)
return(gd)
#EG toGregorian 2436713 -> c(1959,5,24)
#EG toGregorian 2448973 -> c(1992,12,16)
}