Well documented on how to use dates using packages like difftime(), POSIXct(), POSIXlt(), lubridate()

1. Manipulating Dates
Using as.Date, difftime(), as.POSIXct(), as.POSIXlt(),
lubridate()
Rupak Roy

2. #load the data
>datedata<-read.csv(file.choose(),header = TRUE)
>str(datedata)
#using as.Date(): A factor or a character data type can be easily converted into
a date format where as.Date(column_name, orginal_date_format_of the
dataset)
>datedata$Date.received<-as.Date(datedata$Date.received,"%m/%d/%Y")
>datedata$Date.sent.to.company<-
as.Date(datedata$Date.sent.to.company,"%m/%d/%Y")
>str(datedata) #code for identify different combinations of date format
#example:
15/aug/2016:“ %d/%b/%Y ”
13-JUNE-16: “ %d-%B-%y ”
as.Date()
%d Day of the month %m Month (in decimal)
%Y Year (4 digits) %b Month (abbreviated)
%y Year (2 digits) %B Month (full name)

3. #once the data is in date format we can easily extract the months and the
weeks.
>months(datedata$Date.received)
>weekdays(datedata$Date.received)
#even we can filter the data using months() and weekdays()
#sub-setting using base R package
>datadate2<-datedata[(weekdays(datedata$Date.received)=="Sunday"),]
as.Date()
Rupak Roy

4. #using difftime() function we can calculate the time interval / differences
without being converted into minutes, hour, weeks, months or years.
>difftime(time2, time1, tz, units = c("auto", "secs", "mins", "hours", "days",
"weeks"))
Where tz= an optional time zone specification to be used for the conversion
units= Units in which the results are desired.
>difftime(datedata$Date.received,datedata$Date.sent.to.company,units =
"days") #this will give the output in a negative value because we are doing
time1-time2 rather than time2-time1 i.e 5- 10 = -5 rather than 10-5 =5
#therefore
>difftime(datedata$Date.sent.to.company,datedata$Date.received,units =
"days")
To know more about the difftime() function use >?difftime
difftime()

5.  These are date-time conversion functions to manipulate data or the objects
of classes "POSIXlt" and "POSIXct" having time information along with the
date.
 POSIXct is similar to POSIXlt the only difference is POSIXlt stores the data in
a list format
#saving the current date-time information as an example
>datetime<-Sys.time()
>class(datetime)
>weekdays(datetime) >months(datetime)
#convert the date and time into POSIXlt()
>datetime<-as.POSIXlt(datetime)
>datetime$zone >datetime$hour >datetime$wday
as.POSIXct() and as.POSIXlt()
Rupak Roy

6.  Lubridate() is an another function that makes it easier to parse and
manipulate dates.
#install and load the package
>install.packages(lubridate)
>library(lubridate)
>datedata<-read.csv(file.choose(),header = TRUE)
>str(datedata)
#converting the factor data type into date data type
>datedata$Date.received<-mdy(datedata$Date.received)
>str(datedata)
Where, mdy =
lubridate()
Code Format dmy() 3/10/2017
mdy() 10/3/2017 dmy_hm() 3/10/2017 23:40
ydm() 2017/3/10 dmy_hms() mdy_hm() mdy_hms() ydm_hm()

7. Next:
We will learn an another important function that is combining two
or more data sets using merge().
Manipulating Dates
Rupak Roy