Bernard Szlachta at 22:00, 14 February 2017

2017-02-14T22:00:12Z

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[[Category:Intro to R|020]]

== Date format ==
Make sure that the ''hiredate'' in the ''emp'' dataframe is a ''Date'' type
<source lang="rsplus">
str(emp)
</source>
'data.frame': 14 obs. of 8 variables:
$ ID : int 7839 7698 7782 7566 7654 7499 7844 7900 7521 7902
...
$ HIREDATE: '''Date''', format: "1981-11-17" ...
...
$ DEPTNO : int 10 30 10 20 30 30 30 30 30 20

If it is not, covert it to the Date format
emp$HIREDATE <- as.Date(emp$HIREDATE,format="%d/%m/%Y")

== Current Date ==
Get current date, current date and time and the system timezone:
> Sys.Date()
[1] "2012-04-15"
> Sys.time()
[1] "2012-04-15 03:20:45 BST"
> Sys.timezone()
[1] "BST"

== Extracting part of the date ==
Which year do we have?
> format(Sys.Date(),"%Y")
[1] "2012"

Use: %d for day, %m for months and ?Date (mind the upper case "D") for more help

== Calculating Intervals ==

What will be the date in 8 weeks:
> Sys.Date() + as.difftime(8,units="weeks")
[1] "2012-06-10"

What is the employees seniority?
> td <- Sys.Date() - emp$HIREDATE
> data.frame(emp,Seniority=as.double(td/365.24))[,c("ENAME","Seniority")]
ENAME Seniority
1 BUSH 35.24532
2 BLAIR 35.79290
3 MERKEL 35.68612
4 PUTIN 35.87230
5 CHIRACK 35.38221
6 BAROSSO 35.98456
7 GATES 35.43697
8 BUFFETT 35.20151
9 WALTON 35.97908
10 TOOSK 35.20151
11 THATCHER 36.16252
12 CARNEGIE 34.18574
13 FORD 34.09265
14 ELISON 35.06188

== Exercises ==
'''17. Exercise'''

Compute job seniority (use format and as.integer )

ID ENAME JOB MGR HIREDATE SAL COMM DEPTNO Seniority
1 7839 BUSH PRESIDENT NA 1981-11-17 5000 NA 10 31
2 7698 BLAIR MANAGER 7839 1981-05-01 2850 NA 30 31
3 7782 MERKEL MANAGER 7839 1981-06-09 2450 NA 10 31
4 7566 PUTIN MANAGER 7839 1981-04-02 2975 NA 20 31
5 7654 CHIRACK SALESMAN 7698 1981-09-28 1250 1400 30 31
6 7499 BAROSSO SALESMAN 7698 1981-02-20 1600 300 30 31
7 7844 GATES SALESMAN 7698 1981-09-08 1500 0 30 31
8 7900 BUFFETT CLERK 7698 1981-12-03 950 NA 30 31
9 7521 WALTON SALESMAN 7698 1981-02-22 1250 500 30 31
10 7902 TOOSK ANALYST 7566 1981-12-03 3000 NA 20 31
11 7369 THATCHER CLERK 7902 1980-12-17 800 NA 20 32
12 7788 CARNEGIE ANALYST 7566 1982-12-09 3000 NA 20 30
13 7876 FORD CLERK 7788 1983-01-12 1100 NA 20 29
14 7934 ELISON CLERK 7782 1982-01-23 1300 NA 10 30

<div style="color:white">
curyear <- as.integer(format(Sys.Date(),"%Y"))
Seniority <- curyear - as.integer(format(emp$HIREDATE,"%Y"))
cbind(emp,Seniority)
</div>

'''18. *Exercise'''

Compute job seniority (use "-" operator between dates).

+----------+-----------+
| ename | Seniority |
+----------+-----------+
| BUSH | 25.14 |
| BLAIR | 25.69 |
| MERKEL | 25.59 |
| PUTIN | 25.78 |
| CHIRACK | 25.28 |
| BAROSSO | 25.89 |
| GATES | 25.33 |
| BUFFETT | 25.09 |
| WALTON | 25.88 |
| TOOSK | 25.09 |
| THATCHER | 26.07 |
| CARNEGIE | 24.06 |
| FORD | 23.97 |
| ELISON | 24.95 |
+----------+-----------+
<div style="color:white">

td <- Seniority <- Sys.Date() - emp$HIREDATE
cbind(emp,Seniority=td/365.25)[,c("ENAME","Seniority")]
</div>

'''19. Exercise'''

Select employees hired before 1st of April 1981.

+----------+------------+
| ename | hiredate |
+----------+------------+
| BAROSSO | 1981-02-20 |
| WALTON | 1981-02-22 |
| THATCHER | 1980-12-17 |
+----------+------------+

'''20. Exercise'''

Select employees hired in January.
* Method 1: use format() function
* Method 2: use compound condition (date from date to)

+--------+------------+
| ename | hiredate |
+--------+------------+
| FORD | 1983-01-12 |
| ELISON | 1982-01-23 |
+--------+------------+

'''21. Exercise'''

Select the information below. Use ?format if needed.
hint
* apropos("date")
* ?format.Date
* ?strptime

+----------+--------------------------------------------+
| ename | When hired? |
+----------+--------------------------------------------+
| BUSH | was hired 17 of November 1981 Tuesday |
| BLAIR | was hired 1 of May 1981 Friday |
| MERKEL | was hired 9 of June 1981 Tuesday |
| PUTIN | was hired 2 of April 1981 Thursday |
| CHIRACK | was hired 28 of September 1981 Monday |
| BAROSSO | was hired 20 of February 1981 Friday |
| GATES | was hired 8 of September 1981 Tuesday |
| BUFFETT | was hired 3 of December 1981 Thursday |
| WALTON | was hired 22 of February 1981 Sunday |
| TOOSK | was hired 3 of December 1981 Thursday |
| THATCHER | was hired 17 of December 1980 Wednesday |
| CARNEGIE | was hired 9 of December 1982 Thursday |
| FORD | was hired 12 of January 1983 Wednesday |
| ELISON | was hired 23 of January 1982 Saturday |
+----------+--------------------------------------------+

'''22. Exercise*'''

Show all employees hired 50 days before (inclusive) to 50 days after (inclusive) 28th February 1982

+--------+------------+
| ename | hiredate |
+--------+------------+
| ELISON | 1982-01-23 |
+--------+------------+

== POSIX Time Format ==

;POSIXct
# number of seconds since the start of January 1, 1970 (Unix Era)
# negative numbers - before Unix Era

;POSIXlt
Is a vector of:
# seconds
# minutes
# hours
# day of month (1-31)
# month of the year (0-11)
# years since 1900
# day of the week (0-6 where 0 represents Sunday)
# day of the year (0-365)
# daylight savings indicator

== ISOdatetime ==
<source lang="rsplus">
d1 = ISOdate(1982,2,3)
d2 = ISOdate(1981,2,3)
d1-d2
Time difference of 365 days
as.double(d1-d2)
[1] 365
</source>

<source lang="rsplus">
dt1 = ISOdatetime(1982,2,3,2,1,2)
dt2 = ISOdatetime(1982,2,3,12,1,2)
dt1-dt2
</source>
Time difference of -10 hours

== Converting Charater to Time ==

<source lang="rsplus">
d1 <- strptime("2016-01-01 00:00:00","%Y-%m-%d %H:%M:%S")
d2 <- strptime("2016-01-01 01:00:00","%Y-%m-%d %H:%M:%S")
</source>

== Difference between ISOdate and ISOdatetime ==
Effectively ISOdate is ISOdatetime at 12:00:00 GMT
> dt1 <- ISOdate(2016,1,1)
> dt2 <- ISOdate(2016,1,1,12,00,00)
> dt1
[1] "2016-01-01 12:00:00 GMT"
> dt2
[1] "2016-01-01 12:00:00 GMT"

;Presentation of midnight
> d1 <- strptime("2016-01-01 00:00:00","%Y-%m-%d %H:%M:%S")
> d2 <- strptime("2016-01-01 01:00:00","%Y-%m-%d %H:%M:%S")
> d1
[1] "2016-01-01 CST"
> d2
[1] "2016-01-01 01:00:00 CST"

== difftime ==
Subtracting dates in normal ways can be implicitly converted to different number depend on how big is the interval
> dt1 <- ISOdate(2016,1,1,12,00,00)
> dt2 <- ISOdate(2016,1,1,12,00,07)
> dt2 - dt1
Time difference of 7 secs
> as.double(dt2 - dt1)
[1] 7
> dt1 <- ISOdate(2016,1,1,12,00,00)
> dt2 <- ISOdate(2116,1,1,12,00,07)
> dt2 - dt1
Time difference of 36524 days
> as.double(dt2 - dt1)
[1] 36524
> difftime(dt2,dt1)
Time difference of 36524 days
> difftime(dt2,dt1,units="sec")
Time difference of 3155673607 secs

== Setting up timezone ==
ISOdate(2016,1,1,12,00,00,tz = "CST")

R - Dealing with Date and Time - Revision history

Bernard Szlachta at 22:00, 14 February 2017