YouTipJulia Date Time
Julia provides the following three functions to handle dates and times through the Dates module:
* **Date**: represents a date, accurate to the day, displays only the date.
* **DateTime**: represents date and time, accurate to milliseconds.
* **DateTime**: represents date and time, accurate to nanoseconds, representing a specific moment in 24 hours of a day.
Before using, we need to import the Dates module first:
```julia
import Dates
Date and DateTime types can be parsed from integers or Period types.
Period is based on date values, representing years, months, days, etc.:
```julia
Period
Year
Quarter
Month
Week
Day
Hour
Minute
Second
Millisecond
Microsecond
Nanosecond
Date and DateTime are both subtypes of the abstract type TimeType.
The following image shows the relationship between date types, click to enlarge:
[!(#)](#)
Output the time of the date:
## Example
```julia
julia> import Dates
julia> rightnow = Dates.Time(Dates.now())# time
08:41:15.917
julia> theday = Dates.Date(2022,5,6)# date
2022-05-06
julia> today_date = Dates.today()
2022-05-11
julia> Dates.now(Dates.UTC)
2022-05-11T00:44:20.136
# Formatting Time
```julia
julia> Dates.DateTime("20220429 120000", "yyyymmdd HHMMSS")
2022-04-29T12:00:00
julia> Dates.DateTime("19/04/2022 17:42", "dd/mm/yyyy HH:MM")
2022-04-19T17:42:00
The following table gives date format codes, through which we can format our dates:
| Character | Date/Time Element |
| --- | --- |
| Y | Represents year, for example: yyyy => 1984, yy => 84 |
| m | Represents year, for example: m => 7 or 07 |
| u | Represents abbreviated month name, for example: Jun |
| U | Represents full month name, for example: January |
| e | Represents abbreviated day of week, for example: Mon |
| E | Represents full day of week, for example: Monday |
| d | Represents day, for example: 1 or 01 |
| H | Represents hour, for example: HH => 00 |
| M | Represents minute, for example: MM => 00 |
| S | Represents second, for example: S => 00 |
| s | Represents millisecond, for example: .000 |
## Example
```julia
julia> Dates.Date("Sun, 27 Sep 2022", "e, d u y")
2022-09-27
julia> Dates.DateTime("Sun, 27 Sep 2022 10:25:10", "e, d u y H:M:S")
2022-09-27T10:25:10
Through the examples above, we have learned about some date and time objects. Next, we can use these objects to get data (including year, month, day, minute, second, hour, etc.):
## Example
```julia
julia> theday = Dates.Date(2022,5,6)# create date object
2022-05-06
# Next, get the data from theday
julia> Dates.year(theday)
2022
julia> Dates.month(theday)
5
# Get current time data
julia> rightnow = Dates.now()
2022-05-11T08:51:45.342
julia> Dates.minute(rightnow)
51
julia> Dates.hour(rightnow)
8
julia> Dates.second(rightnow)
45
# Get month and day of week
julia> Dates.dayofweek(theday)
5
julia> Dates.dayname(theday)
"Friday"
julia> Dates.yearmonthday(theday)
(2022, 5, 6)
julia> Dates.dayofweekofmonth(theday)
1
### Date Operations
We can perform arithmetic operations on date objects.
For example, we calculate how many days difference between two dates:
## Example
```julia
julia> day1 = Dates.Date(2022,1,17)
2022-01-17
julia> day2 = Dates.Date(2022,3,23)
2022-03-23
julia> day2 - day1
65 days
# Using different time units
julia> Dates.canonicalize(Dates.CompoundPeriod(day2 - day1))
9 weeks, 2 days
We can also add to dates, for example, calculating the date after 2 years and 6 months:
## Example
```julia
julia> rightnow = Dates.now()
2022-05-11T09:01:07.946
julia> rightnow + Dates.Year(20) + Dates.Month(6)
2042-11-11T09:01:07.946
# Date after 6 days
julia> rightnow + Dates.Day(6)
2022-05-17T09:01:07.946
### Date Range
Julia can create dates for a specified range through iterable range objects. In the example below, we will create an iterator that generates the first day of each month.
## Example
```julia
date_range = Dates.Date(2011,1,1):Dates.Month(1):Dates.Date(2022,1,1)
Dates.Date("2011-01-01"):Dates.Month(1):Dates.Date("2022-01-01")
In the above range object, we can find which ones are weekdays. Here we need to create an anonymous function for filter(), which will determine whether a given date is a weekday:
## Example
```julia
julia> weekdaysfromrange = filter(dy -> Dates.dayname(dy)!= "Saturday"&& Dates.dayname(dy)!= "Sunday" , date_range)
94-element Vector{Dates.Date}:
2011-02-01
2011-03-01
2011-04-01
2011-06-01
2011-07-01
2011-08-01
2011-09-01
2011-11-01
2011-12-01
2012-02-01
⋮
2021-02-01
2021-03-01
2021-04-01
2021-06-01
2021-07-01
2021-09-01
2021-10-01
2021-11-01
2021-12-01
### Rounding Dates and Time
We often use round(),