datetime.utf8

Agenda

get current date/time
understand date/time classes in R
date arithmetic
timezones & daylight savings
date/time formats
date/time parsing
date/time components
create, update & verify date/time objects
intervals, duration and period

Prerequisites

completed Introduction to R course
laptop/desktop with R & RStudio installed
internet connection to use RStudio Cloud

Resources

Current Date/Time

Function	Description
`Sys.Date()`	Current Date
`lubridate::today()`	Current Date
`Sys.time()`	Current Time
`lubridate::now()`	Current Time
`lubridate::am()`	Whether time occurs in am?
`lubridate::pm()`	Whether time occurs in pm?
`lubridate::leap_year()`	Check if the year is a leap year?

Your Turn

get current date
get current time
check whether the time occurs in am or pm?
check whether the following years were leap years
- 2018
- 2016

Case Study - Data

transact <- read_csv('https://raw.githubusercontent.com/rsquaredacademy/datasets/master/transact.csv')

## # A tibble: 2,466 x 3
##    Invoice    Due        Payment   
##    <date>     <date>     <date>    
##  1 2013-01-02 2013-02-01 2013-01-15
##  2 2013-01-26 2013-02-25 2013-03-03
##  3 2013-07-03 2013-08-02 2013-07-08
##  4 2013-02-10 2013-03-12 2013-03-17
##  5 2012-10-25 2012-11-24 2012-11-28
##  6 2012-01-27 2012-02-26 2012-02-22
##  7 2013-08-13 2013-09-12 2013-09-09
##  8 2012-12-16 2013-01-15 2013-01-12
##  9 2012-05-14 2012-06-13 2012-07-01
## 10 2013-07-01 2013-07-31 2013-07-26
## # ... with 2,456 more rows

Case Study

extract date, month and year from Due
compute the number of days to settle invoice
compute days over due
check if due year is a leap year
check when due day in february is 29, whether it is a leap year
how many invoices were settled within due date
how many invoices are due in each quarter
what is the average duration between invoice date and payment date

Date/Time Classes

Date
POSIXct
POSIXlt

ISO 8601 Format

POSIXlt

Component	Description
`sec`	Second
`min`	Minute
`hour`	Hour of the day
`mon`	Month of the year (0-11
`zone`	Timezone
`wday`	Day of week
`mday`	Day of month
`year`	Years since 1900
`yday`	Day of year
`isdst`	Daylight saving flag
`gmtoff`	Offset is seconds from GMT

Your Turn

R 1.0.0 was released on 2000-02-29 08:55:23 UTC. Save it as

Date using character
Date using origin and number
POSIXct
POSIXlt and extract
- month day
- day of year
- month
- zone
ISODate

Date Arithmetic - Course Length

Date Arithmetic - Shift Date

Your Turn

compute the length of a vacation which begins on 2020-04-19 and ends on 2020-04-25
recompute the length of the vacation after shifting the vacation start and end date by 10 days and 2 weeks
compute the days to settle invoice and days overdue from the receivables.csv data set
compute the length of employment (only for those employees who have been terminated) from the hr-data.csv data set (use date of hire and termination)

Timezones

Daylight Savings

Your Turn

check the timezone you live in
check if daylight savings in on
check the current time in UTC or a different time zone

Date & Time Formats

December 12, 2019"
12th Dec, 2019
Dec 12th, 19
12-Dec-19
2019 December
12.12.19

Conversion Specifications

Specification	Description	Example
`%d`	Day of the month (decimal number)	12
`%m`	Month (decimal number)	12
`%b`	Month (abbreviated)	Dec
`%B`	Month (full name)	December
`%y`	Year (2 digit)	19
`%Y`	Year (4 digit)	2019
%H	Hour	8
%M	Minute	5
%S	Second	3

Your Turn

Below, we have specified July 5th, 2019 in different ways. Create the date using as.Date() while specifying the correct format for each of them.

05.07.19
5-July 2019
July 5th, 2019
July 05, 2019
2019-July- 05
05/07/2019
07/05/2019
7/5/2019
07/5/19
2019-07-05

Parse Date & Time

Date	Specification
19-07-05	`ymd`
2019-07-05	`ymd`
05-07-2019	`dmy`
07-05-2019	`mdy`

Your Turn

Below, we have specified July 5th, 2019 in different ways. Parse the dates using strptime() or parse_date_time() or any other helper function.

July-05-19
JUL-05-19
05.07.19
5-July 2019
July 5th, 2019
July 05, 2019
2019-July- 05
05/07/2019
07/05/2019
7/5/2019
2019-07-05

Date & Time Components

year
month
date
week
day
quarter
semester
hour
minute
second
timezone

Year, Month & Week

Function	Description
`year()`	Get year
`month()`	Get month (number)
`month(label = TRUE)`	Get month (abbreviated name)
`month(abbr = FALSE)`	Get month (full name)
`months()`	Get month
`week()`	Get week

Day

Function	Description
`day`	Get day
`mday()`	Day of the month
`wday()`	Day of the week
`qday()`	Day of quarter
`yday()`	Day of year
`weekdays()`	Day of week
`days_in_month()`	Days in the month

Hour, Minute & Seconds

Function	Description
`hour()`	Get hour
`minute()`	Get minute
`second()`	Get second
`seconds()`	Number of seconds since `1970-01-01`

Quarter & Semester

Function	Description
`quarter()`	Get quarter
`quarter(with_year = TRUE)`	Quarter with year
`quarter(fiscal_start = 4)`	Fiscal starts in April
`quarters()`	Get quarter
`semester()`	Get semester

Case Study - Day, Month & Year

Case Study - Data Sanitization

Let us do some data sanitization. If the due day happens to be February 29, let us ensure that the due year is a leap year. Below are the steps to check if the due year is a leap year:

we will extract the following from the due date:
- day
- month
- year
we will then create a new column is_leap which will have be set to TRUE if the year is a leap year else it will be set to FALSE
filter all the payments due on 29th Feb
select the following columns:
- Due
- is_leap

Your Turn

Get the R release dates using r_versions() from the rversions package and tabulate the following

year
month with label
weekday with label
hour
and quarter

Create, Update & Verify

make_date()
make_datetime()
update()

Date Sequence

Function	Description
`from`	Starting date of the sequence
`by`	End date of the sequence
`to`	Date increment of the sequence
`length.out`	Length of the sequence
`along.with`	Use length of this value as length of sequence

Your Turn

R 2.0.0 was released on 2004-10-04 14:24:38. Create this date using

make_date()
make_datetime()
and update to 2013-04-03 07:12:36 (R 3.0.0 release date)

Interval

Shift Interval

Interval Overlap

Case Study

Let us use intervals to count the number of invoices that were settled within the due date. To do this, we will:

create an interval for the invoice and due date
create a new column due_next by incrementing the due date by 1 day
another interval for due_next and the payment date
if the intervals overlap, the payment was made within the due date

Within

Case Stduy

Let us use %within% to count the number of invoices that were settled within the due date. We will do this by:

creating an interval for the invoice and due date
check if the payment date falls within the above interval

Duration

Period

Time Length

Rounding Dates

We will explore functions for rounding dates

to the nearest value using round_dates()
down using floor_date()
up using ceiling_date()

Rounding Dates

The unit for rounding can be any of the following:

second
minute
hour
day
week
month
bimonth
quarter
season
halfyear
and year

Your Turn

round up R release dates to hours
round down R release dates to minutes
rollback R release dates to the beginning of the month

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