Date Time

---

Sys.Date

To know current date:

> Sys.Date()

[1] "2020-12-30"

To know current date as well as time and timezone:

> Sys.time()

[1] "2020-12-30 22:02:59 +06"

To show in a good form use the following formats:

• %y shows 2-digit year. For example: 97
• %Y shows 4-digit year. For example: 1997
• %d shows day as a number from 0-31
• %a shows abbreviated weekday e.g. Mon
• %A unabbreviated weekday e.g. Monday
• %m shows months in number i.e. (00-12)
• %b shows abbreviated month e.g. Jan
• %B shows unabbreviated month e.g. January

To know more run help(strftime).

> format(Sys.time(), "%d %B %Y")

[1] "30 December 2020"

> format(Sys.time(), "%B %d, %Y")

[1] "December 30, 2020"

> format(Sys.time(), "%X")

[1] "10:02:59 PM"

> format(Sys.time(), "%Z")

[1] "+06"

date()

date() shows the current date and time -

> date()[1]

[1] "Wed Dec 30 22:02:59 2020"

as.Date()

The default format is yyyy-mm-dd.

use as.Date( ) to convert strings to dates

> as.Date(c("2020-01-20", "2020-01-30"))

[1] "2020-01-20" "2020-01-30"

To see the difference between dates -

> as.Date("2020-01-30") - as.Date("2020-01-21")

Time difference of 9 days

We can use formats to specify how to read the date from character -

> today <- "28/09/2020"
> today

[1] "28/09/2020"

> class(today)

[1] "character"

> new_today <- as.Date(today, "%d/%m/%y")
> new_today

[1] "2020-09-28"

> class(new_today)

[1] "Date"

Sequence of dates

Sequence of months

> start_date <- as.Date("2020-01-01")
> end_date <- as.Date("2022-12-31")
> seq(start_date, end_date, by="+1 months")

 [1] "2020-01-01" "2020-02-01" "2020-03-01" "2020-04-01" "2020-05-01"
 [6] "2020-06-01" "2020-07-01" "2020-08-01" "2020-09-01" "2020-10-01"
[11] "2020-11-01" "2020-12-01" "2021-01-01" "2021-02-01" "2021-03-01"
[16] "2021-04-01" "2021-05-01" "2021-06-01" "2021-07-01" "2021-08-01"
[21] "2021-09-01" "2021-10-01" "2021-11-01" "2021-12-01" "2022-01-01"
[26] "2022-02-01" "2022-03-01" "2022-04-01" "2022-05-01" "2022-06-01"
[31] "2022-07-01" "2022-08-01" "2022-09-01" "2022-10-01" "2022-11-01"
[36] "2022-12-01"

> seq(end_date, start_date, by="-1 months")

 [1] "2022-12-31" "2022-12-01" "2022-10-31" "2022-10-01" "2022-08-31"
 [6] "2022-07-31" "2022-07-01" "2022-05-31" "2022-05-01" "2022-03-31"
[11] "2022-03-03" "2022-01-31" "2021-12-31" "2021-12-01" "2021-10-31"
[16] "2021-10-01" "2021-08-31" "2021-07-31" "2021-07-01" "2021-05-31"
[21] "2021-05-01" "2021-03-31" "2021-03-03" "2021-01-31" "2020-12-31"
[26] "2020-12-01" "2020-10-31" "2020-10-01" "2020-08-31" "2020-07-31"
[31] "2020-07-01" "2020-05-31" "2020-05-01" "2020-03-31" "2020-03-02"
[36] "2020-01-31"

> seq(as.Date("2020-01-01"), by="months", length=6)

[1] "2020-01-01" "2020-02-01" "2020-03-01" "2020-04-01" "2020-05-01"
[6] "2020-06-01"

Sequence of years

> seq(as.Date("2020-01-01"), as.Date("2022-12-31"), by = "+1 years")

[1] "2020-01-01" "2021-01-01" "2022-01-01"

> seq(as.Date("2020-01-01"), by="years", length=6)

[1] "2020-01-01" "2021-01-01" "2022-01-01" "2023-01-01" "2024-01-01"
[6] "2025-01-01"

Sequence of days

> seq(as.Date("2020-01-01"), as.Date("2020-01-31"), by = "+7 days")

[1] "2020-01-01" "2020-01-08" "2020-01-15" "2020-01-22" "2020-01-29"

> seq(as.Date("2020-01-01"), by="days", length=7)

[1] "2020-01-01" "2020-01-02" "2020-01-03" "2020-01-04" "2020-01-05"
[6] "2020-01-06" "2020-01-07"

To know in detail visit this bookdown site and statsmethod.net

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