Base Functions: Date in R

Sys.Date()  
format.Date() # simply format()
weekdays()
seq.Date()
as.Date()

Sys.Date()

# Current Date and Time
Sys.Date()

## [1] "2025-08-20"

Sys.time()

## [1] "2025-08-20 10:23:56 +03"

today <- Sys.Date()

today

## [1] "2025-08-20"

Base Functions: Date in R

format.Date() # simply format()
weekdays()
seq.Date()
as.Date()

format()

today

## [1] "2025-08-20"

format(today, "%d %m %y")

## [1] "20 08 25"

format.Date(today, "%d %m %y")

## [1] "20 08 25"

format(today, "%d %m %y")

## [1] "20 08 25"

format.Date(today, "%d/%m/%y")

## [1] "20/08/25"

format.Date(today, "%d-%m-%y")

## [1] "20-08-25"

Base Functions: Date in R

format.Date() # simply format()
weekdays()
seq.Date()
as.Date()

format()

Code	Value
`%d`	Day of month as number
`%m`	Month as number
`%b`	Month abbreviated
`%B`	Month full name
`%y`	Year, two digits
`%Y`	Year, four digits

format(today, "%d %b %y")  # with month abbreviated

## [1] "20 Aug 25"

format(today, "%d %B %y")  # with month full name

## [1] "20 August 25"

format(today, "%d %B %Y")  # with month full name

## [1] "20 August 2025"

Base Functions: Date in R

as.Date() 
weekdays()
seq.Date()

as.Date() Function

as.Date(c("04-28-2015", "11-12-2016"), format = "%m-%d-%Y")

## [1] "2015-04-28" "2016-11-12"

x <- as.Date(c("04-28-2015", "11-12-2016"), format = "%m-%d-%Y")
str(x)

##  Date[1:2], format: "2015-04-28" "2016-11-12"

format(x, "%d %B %Y")

## [1] "28 April 2015"    "12 November 2016"

format(x, "%B %d, %Y")

## [1] "April 28, 2015"    "November 12, 2016"

Base Functions: Date in R

as.Date() 
weekdays()
seq.Date()

as.Date() Function

as.Date(c("07/14/17"), format = "%m/%d/%y")

## [1] "2017-07-14"

x <- c("1jan1960", "2jan1960", "31mar1960", "30jul1960")
x

## [1] "1jan1960"  "2jan1960"  "31mar1960" "30jul1960"

str(x)

##  chr [1:4] "1jan1960" "2jan1960" "31mar1960" "30jul1960"

z <- as.Date(x, "%d%b%Y")
z

## [1] "1960-01-01" "1960-01-02" "1960-03-31" "1960-07-30"

str(z)

##  Date[1:4], format: "1960-01-01" "1960-01-02" "1960-03-31" "1960-07-30"

Base Functions: Date in R

as.Date() 
weekdays()
seq.Date()

strptime() Function

# number of days since origin time.. 
as.Date(32768, origin = "1900-01-01") # number of days since 1900

## [1] "1989-09-19"

# a complex one - with time
datestring <- c("January 10, 2012 10:40", "December 9, 2011 9:10")
datestring

## [1] "January 10, 2012 10:40" "December 9, 2011 9:10"

# strptime() function
(datestring_d <- strptime(datestring, "%B %d, %Y %H:%M"))

## [1] "2012-01-10 10:40:00 EET" "2011-12-09 09:10:00 EET"

str(datestring)

##  chr [1:2] "January 10, 2012 10:40" "December 9, 2011 9:10"

str(datestring_d)

##  POSIXlt[1:2], format: "2012-01-10 10:40:00" "2011-12-09 09:10:00"

as.Date(datestring_d)

## [1] "2012-01-10" "2011-12-09"

Base Functions: Date in R

weekdays()
seq.Date()

weekdays() Function

Sys.Date()

## [1] "2025-08-20"

weekdays(Sys.Date())

## [1] "Wednesday"

weekdays(Sys.Date() + 1:10)

##  [1] "Thursday"  "Friday"    "Saturday"  "Sunday"    "Monday"    "Tuesday"  
##  [7] "Wednesday" "Thursday"  "Friday"    "Saturday"

## [1] "1960-01-01" "1960-01-02" "1960-03-31" "1960-07-30"

weekdays(z)

## [1] "Friday"   "Saturday" "Thursday" "Saturday"

z[weekdays(z)=="Saturday"]

## [1] "1960-01-02" "1960-07-30"

z[weekdays(z) %in% c("Saturday", "Friday")]

## [1] "1960-01-01" "1960-01-02" "1960-07-30"

Base Functions: Date in R

seq.Date()

seq.Date() Function

# by= one of the ("day", "week", "month", "quarter" or "year")

seq.Date(from=as.Date("2023/1/1"), to=as.Date("2025/1/1"), by="quarter")

## [1] "2023-01-01" "2023-04-01" "2023-07-01" "2023-10-01" "2024-01-01"
## [6] "2024-04-01" "2024-07-01" "2024-10-01" "2025-01-01"

seq.Date(from=as.Date("2023/1/1"), to=as.Date("2023/4/1"), by="month")

## [1] "2023-01-01" "2023-02-01" "2023-03-01" "2023-04-01"

seq.Date(from=as.Date("2023/4/1"), to=as.Date("2023/1/1"), by="-1 month")

## [1] "2023-04-01" "2023-03-01" "2023-02-01" "2023-01-01"

# length.out = number
seq.Date(from=as.Date("2020/1/1"), length.out = 5, by="quarter")

## [1] "2020-01-01" "2020-04-01" "2020-07-01" "2020-10-01" "2021-01-01"

# both by and length.out
seq.Date(from=as.Date("2020/1/1"), length.out = 5, by="month")

## [1] "2020-01-01" "2020-02-01" "2020-03-01" "2020-04-01" "2020-05-01"

Base Functions: Date in R

seq.Date()

seq.Date() Function

(x <- as.Date("1jan1960", format = "%d%b%Y"))

## [1] "1960-01-01"

seq(from = x, length = 6, by = "week")

## [1] "1960-01-01" "1960-01-08" "1960-01-15" "1960-01-22" "1960-01-29"
## [6] "1960-02-05"

weekdays(seq(from = x, length = 6, by = "week"))

## [1] "Friday" "Friday" "Friday" "Friday" "Friday" "Friday"

weekdays(seq(from = x, length = 6, by = "day"))

## [1] "Friday"    "Saturday"  "Sunday"    "Monday"    "Tuesday"   "Wednesday"

weekdays(seq(from = x, length = 6, by = "month"))

## [1] "Friday"    "Monday"    "Tuesday"   "Friday"    "Sunday"    "Wednesday"

# change to numeric
as.numeric(x)

## [1] -3653

# teaser, subtraction
x - as.Date("1970-01-01")

## Time difference of -3653 days

Basic Operations: Subtraction, Addition and Comparison

x <- as.Date("May 05, 2023", format = "%B %d, %Y")
x

## [1] "2023-05-05"

y <- as.Date("March 5, 2023", format = "%B %d, %Y")
y

## [1] "2023-03-05"

# subtraction: number of days 
x - y

## Time difference of 61 days

y - x

## Time difference of -61 days

x - seq(from = y, length = 6, by = "week")

## Time differences in days
## [1] 61 54 47 40 33 26

# adding and subtracting number
x + 1

## [1] "2023-05-06"

x - 1

## [1] "2023-05-04"

# comparisons 
x > y

## [1] TRUE

y > x

## [1] FALSE

`ts` Objects

ts objects

ts(data = NA, start = 1, end = numeric(), frequency = 1,
   deltat = 1, ts.eps = getOption("ts.eps"), class = , names = ) 

as.ts()  
is.ts()

Important Function Arguments:
- data: Observed Values
- start: the time of the first observation
- frequency: the number of observations per unit of time

`ts` Object Examples

first_ts <- ts(1:10, frequency = 4, start = c(1959, 2))
first_ts

##      Qtr1 Qtr2 Qtr3 Qtr4
## 1959         1    2    3
## 1960    4    5    6    7
## 1961    8    9   10

print(first_ts)

##      Qtr1 Qtr2 Qtr3 Qtr4
## 1959         1    2    3
## 1960    4    5    6    7
## 1961    8    9   10

print(first_ts, calendar = F)

## Time Series:
## Start = c(1959, 2) 
## End = c(1961, 3) 
## Frequency = 4 
##  [1]  1  2  3  4  5  6  7  8  9 10

# column wise
matrix(data=1:12,nrow=3)

##      [,1] [,2] [,3] [,4]
## [1,]    1    4    7   10
## [2,]    2    5    8   11
## [3,]    3    6    9   12

# row wise
matrix(data=1:12,nrow=3, byrow = TRUE)

##      [,1] [,2] [,3] [,4]
## [1,]    1    2    3    4
## [2,]    5    6    7    8
## [3,]    9   10   11   12

# without column names
ts(matrix(1:20, nrow = 5), start = c(1961, 1), frequency = 12)

##          Series 1 Series 2 Series 3 Series 4
## Jan 1961        1        6       11       16
## Feb 1961        2        7       12       17
## Mar 1961        3        8       13       18
## Apr 1961        4        9       14       19
## May 1961        5       10       15       20

# with column names
second_ts <- ts(matrix(1:20, 5), start = c(1961, 1), frequency = 12,
   names = c("x_1","x_2","x_3","x_4"))

second_ts

##          x_1 x_2 x_3 x_4
## Jan 1961   1   6  11  16
## Feb 1961   2   7  12  17
## Mar 1961   3   8  13  18
## Apr 1961   4   9  14  19
## May 1961   5  10  15  20

is.ts(second_ts)

## [1] TRUE

is.ts(first_ts)

## [1] TRUE

Useful Functions for `ts` Objects

tsp() 
frequency()  
start()
end()
time()
window()
plot.ts() # only example

tsp(first_ts)

## [1] 1959.25 1961.50    4.00

# first: 1959.25, second: 1961.50 freq: 4.00

tsp(second_ts)

## [1] 1961.000 1961.333   12.000

frequency(first_ts)

## [1] 4

frequency(second_ts)

## [1] 12

time(second_ts)

##           Jan      Feb      Mar      Apr      May
## 1961 1961.000 1961.083 1961.167 1961.250 1961.333

time(first_ts)

##         Qtr1    Qtr2    Qtr3    Qtr4
## 1959         1959.25 1959.50 1959.75
## 1960 1960.00 1960.25 1960.50 1960.75
## 1961 1961.00 1961.25 1961.50

# windowing 
window(second_ts, start=c(1961,2))

##          x_1 x_2 x_3 x_4
## Feb 1961   2   7  12  17
## Mar 1961   3   8  13  18
## Apr 1961   4   9  14  19
## May 1961   5  10  15  20

window(second_ts, start=c(1961,2), end=c(1961,6))

##          x_1 x_2 x_3 x_4
## Feb 1961   2   7  12  17
## Mar 1961   3   8  13  18
## Apr 1961   4   9  14  19
## May 1961   5  10  15  20

# extend the time series
window(second_ts, start=c(1961,2), end=c(1962,5), extend=TRUE)

##          x_1 x_2 x_3 x_4
## Feb 1961   2   7  12  17
## Mar 1961   3   8  13  18
## Apr 1961   4   9  14  19
## May 1961   5  10  15  20
## Jun 1961  NA  NA  NA  NA
## Jul 1961  NA  NA  NA  NA
## Aug 1961  NA  NA  NA  NA
## Sep 1961  NA  NA  NA  NA
## Oct 1961  NA  NA  NA  NA
## Nov 1961  NA  NA  NA  NA
## Dec 1961  NA  NA  NA  NA
## Jan 1962  NA  NA  NA  NA
## Feb 1962  NA  NA  NA  NA
## Mar 1962  NA  NA  NA  NA
## Apr 1962  NA  NA  NA  NA
## May 1962  NA  NA  NA  NA

window(first_ts, start=c(1960,1), end=c(1961,1))

##      Qtr1 Qtr2 Qtr3 Qtr4
## 1960    4    5    6    7
## 1961    8

# modify the values 
window(first_ts, start=c(1960,1), end=c(1960,3)) <- NA

first_ts

##      Qtr1 Qtr2 Qtr3 Qtr4
## 1959         1    2    3
## 1960   NA   NA   NA    7
## 1961    8    9   10

plot(first_ts)

plot(second_ts)

plot(second_ts, plot.type="single", lty=1:4, xlab="X", ylab="Y",
     main="My First Multi-variate Time Series Plot")

Navigate Wikipedia for ISO 8601 Standard

ISO 8601: Wikipedia

Time in R

POSIXct Class

Sys.timezone()

## [1] "Europe/Istanbul"

x <- Sys.Date()
str(x)

##  Date[1:1], format: "2025-08-20"

x_1 <- as.POSIXct(x)
x_1

## [1] "2025-08-20 UTC"

x <- Sys.time()
str(x)

##  POSIXct[1:1], format: "2025-08-20 10:23:56"

x_p <- as.POSIXlt(x)
str(x_p)

##  POSIXlt[1:1], format: "2025-08-20 10:23:56"

names(unclass(x_p))

##  [1] "sec"    "min"    "hour"   "mday"   "mon"    "year"   "wday"   "yday"  
##  [9] "isdst"  "zone"   "gmtoff"

x_p$sec

## [1] 56.92476

x_p$hour

## [1] 10

Introduction to Date and Time in R

References

Before Start: Videos

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Basic Operations: Subtraction, Addition and Comparison

`ts` Objects

`ts` Object Examples

Useful Functions for `ts` Objects

Navigate Wikipedia for ISO 8601 Standard

Time in R

An Important Package: `lubridate` Package

Introduction to Date and Time in R

References

Before Start: Videos

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Base Functions: Date in R

Basic Operations: Subtraction, Addition and Comparison

ts Objects

ts Object Examples

Useful Functions for ts Objects

Navigate Wikipedia for ISO 8601 Standard

Time in R

An Important Package: lubridate Package

`ts` Objects

`ts` Object Examples

Useful Functions for `ts` Objects

An Important Package: `lubridate` Package