RinAction - R Data Manipulation - Date Variable

gistfile1.r

##############################################################  
##       ------------ Date Values -------------             
## Dates are typically entered into R as character strings  
## and then translated into date variables that are stored  
## numerically                                              
## 
## Date format
## %d       --> Day as a number (0-31)
## %a       --> Abbreviated weekday (Mon, Tue, Fri)
## %A       --> Unabbreviated weekday (Monday, Tuesday)
## %m       --> Month (00-12) 
## %b       --> Abbreviated month (Jan, Feb, Mar)
## %B       --> Unabbreviated month (January, Feburary)
## %y       --> 2-digit year (07)
## %Y       --> 4-digit year (2007)
##############################################################


###########################################
# Converting Characters to Date variables
###########################################
# Default date format is YYYY-MM-DD
mydates <- as.Date(c("2007-06-22", "2004-02-13"))
mydates

# Converting character values to dates using various format
strDates <- c("01/05/1965", "08/16/1975")
dates <- as.Date(strDates, "%m/%d/%Y")
dates

myformat <- "%m/%d/%y"
leadership$date
leadership$date <- as.Date(leadership$date, myformat)

###########################################
# Converting Date variables to Characters 
###########################################
strDates <- as.character(dates)
strDates

######################
#Useful date functions
######################
Sys.Date()
date()

today <- Sys.Date()
format(today, format = "%B %d %Y")
format(today, format = "%A")

######################
# Time Difference
######################

# Method 1
startdate <- as.Date("2004-02-13")
enddate <- as.Date("2009-06-22")
days <- enddate - startdate

# Method 2 - Using difftime() function
today <- Sys.Date()
dob <- as.Date("1956-10-10")
difftime(today, dob, units="days")
difftime(today, dob, units="week")
difftime(today, dob, units="mins")