#   EXAMPLES OF USING chron() and as.Date()
#   --------------------------------------------

library(chron)
library(Hmisc)

#   CREATING A FILE
#   --------------------------------------------

outFile <- file("tmp.txt", open="wt")
cat("subject, rd, bd, regist.time, weight\n", file=outFile)
cat("\"100000\", \"02-28-2004\", \"2282003\", \"12:10:01\", \"13\"\n", file=outFile)
cat("\"100000\", \"06-15-2004\", \"2282003\", \"12:10:01\", \"13.5\"\n", file=outFile)
cat("\"222000\", \"11-05-2004\", \"11052003\", \"05:45:05\", \"15\"\n", file=outFile)
cat("\"222000\", \"11-05-2004\", \"11052003\", \"05:45:05\", \"14.1\"\n", file=outFile)
cat("\"300033\", \"08-17-2001\", \"8172000\", \"18:33:31\", \"18\"\n", file=outFile)
cat("\"300033\", \"\", \"8172000\", \"18:33:31\", \"18.7\"\n", file=outFile)
close(outFile)

#   CREATING CHRON OBJECTS
#   --------------------------------------------

datestr = c("02-28-2004","11-05-2004","08-17-2001",NA)
timestr = c("12:10:01","05:45:05","18:33:31","18:33:31")
date = chron(dates=datestr, format="m-d-Y")
time = chron(times=timestr, format="h:m:s")
datetime = chron(dates=date, times=time)

#   MINUS PLUS  <  == 
#   --------------------------------------------
datetime1 - datetime
date1 = date + c(40, 91, 2, 30)
datetime1 = chron(dates=date1, times=time)
date1>date
datetime1==datetime

#   DIFF SORT
#   --------------------------------------------
diff(datetime)
sort(datetime)

#   MINIMUM
#   --------------------------------------------
min(date)
min(date, na.rm=TRUE)

#useful operation: find an earliest date for a certain subject
data = csv.get("tmp.txt")
data$rd = as.character(data$rd)
data$rd = dates(data$rd, format="m-d-Y", out.format="year-m-d")
data
t = tapply(data$rd, data$subject, min, na.rm=TRUE)
t
class(t); class(t[1])
#unfortunately have to work on restoring the "dates" class
ct = chron(dates=t, out.format="year-m-d")
ct

#   AS CHARACTER 
#   --------------------------------------------
datetime
date
time
as.character(datetime)
as.character(date)
as.character(time)

#   AS NUMERIC
#   --------------------------------------------
as.numeric(datetime)
as.numeric(date)
as.numeric(time)

#   IS NA
#   --------------------------------------------
is.na(datetime)

#   SUMMARY
#   --------------------------------------------
summary(datetime)
summary(date)
summary(time)

#   PLOT & LINES 
#   --------------------------------------------
plot(date, c(1,2,2.3,2.9))
lines(date, c(1,2,2.3,2.9))

#   DAYS MONTHS QUATERS YEARS WEEKS WEEKDAYS
#   --------------------------------------------
# for "dates" it works the same way
days(datetime)
months(datetime)
quarters(datetime)
years(datetime)
weekdays(datetime)

#   HOURS MINUTES SECONDS
#   --------------------------------------------
hours(datetime)
hours(time)
hours(date)
minutes(datetime)
seconds(datetime)



#   DATE CLASS Hmisc WORKS WITH
#   --------------------------------------------
data = csv.get("tmp.txt",
               datevars=c("rd"),
               dateformat="%m-%d-%Y")
data$rd
class(data$rd)

#does not work:
#data <- csv.get("tmp.txt",
#                datevars=c("bd"),
#                dateformat=c("%m%d%Y"))
#does not work: the dates are supposed to have the same format
#data <- csv.get("tmp.txt",
#                datevars=c("rd", "bd"),
#                dateformat=c("%m-%d-%Y", "%m%d%Y"))

#to get around this problem: to convert data$db to date:
data$bd = as.character(data$bd)
data$bd = ifelse(nchar(data$bd)==7, paste("0",data$bd,sep=""), data$bd)
data$bd = as.character(strptime(data$bd, "%m%d%Y"))
data$bd = as.Date(data$bd)

data$bd
class(data$bd)

#   CONVERT from class "dates" "times" to "Date"
#   --------------------------------------------
data$bd = chron(dates=as.character(data$bd), format="Y-m-d", out.format="year-mon-day")
data$bd

#   CONVERT from class "Date" to "dates" "times"
#   --------------------------------------------
data$bd = as.Date(data$bd)
data$bd


# NOTE:
# ----------------------------------------------
#1.       format string is different in chron() and as.Date()
#2.       not all functions defined for chron objects are covered here
#3.       sasxport.get() (from Hmisc) uses both as.Date() and chron()
#                 it probably depends on the the SAS format.

# BONUS: (a little bit heavy bonus - only if you really need it)
# ----------------------------------------------
# how to find out a weight measured at the earliest date
#varMin <- function(data, arg, var)
#{
#  argMin = min(data[,arg], na.rm=TRUE)
#  varMin = data[!is.na(data[,var]),var][data[,arg]==argMin]
#  return(ifelse(length(varMin)>1, mean(varMin, na.rm=TRUE), varMin))
#}
#x = with(data, cbind(subject, rd, weight))
#t = mApply(x, x[,"subject"], FUN=varMin, arg="rd", var="weight")
#newD = data.frame(subject=as.numeric(names(t)), startweight=t)

# REMOVING TEMPORARY FILE (platform specific command)
# ---------------------------------------------------

if (.Platform$OS.type == "unix"){
  system(paste("rm", tmpFile))
}else{
  if (.Platform$OS.type == "windows"){
    shell(paste("del", tmpFile))
  }
}