Ruby DateTime Examples: require date

DateTime. Dates and times are complex.

The DateTime class in Ruby helps make them easier. We use it to create, to store, to manipulate dates.

With this class, we get the current date and relative dates. We use special operators to adjust days and months. We can even check for leap years.

An example. This program gets the current date with DateTime.now. It also shows how to access the month, day and year parts of the DateTime.

Note: When this program was run, it was the last day of March. The output shows the correct values.

Month: This returns the numeric form of the month. So January will be equal to 1. And December will be equal to 12.

Day: This returns the numeric day integer. The first day of the month is 1. The last day depends on the month in question.

Year: The year is also stored in integer representation. It contains the full year number, not a shortened form.

Based on:

Ruby 2

Ruby program that uses DateTime.now

require "date"

# Get current date.
current = DateTime.now

# Print current month, day and year.
print "Month: ", current.month, "\n"
print "  Day: ", current.day, "\n"
print " Year: ", current.year, "\n"

Output

Month: 3
  Day: 31
 Year: 2013

Add, subtract. We can add or subtract an integer from a Date. Subtracting one yields the previous day, and adding one moves to the next day. In this way, we compute yesterday and tomorrow.

Note: Only integers are supported here. If you try adding or subtracting a floating-point number, the fractional part is ignored.

Ruby program that adds, subtracts days

require "date"

# First day of 2014.
d = Date.new(2014, 1, 1)

# Subtract one day to get the last day of 2013.
subtract = d - 1

# Add one day to get the next day.
add = d + 1

# Display values.
puts subtract
puts d
puts add

Output

2013-12-31
2014-01-01
2014-01-02

Gm, local. We create arbitrary times with the Time.gm and Time.local methods. Time.gm returns a UTC time. Time.local returns a time adjusted for your local time zone.

Here: In this program, I pass the year, month, and day to these methods. These are the first three arguments.

Further: We can pass more arguments to Time.gm to increase the accuracy of your time. Here I pass 6.

Mktime: This has the same effect as local. If it is easier for you to remember mktime, then you can use it instead.

Ruby program that uses gm, local

# Create a UTC time for the specified values.
t = Time.gm(2013, "mar", 15)
puts t

# Create time with local time zone.
t = Time.local(2010, "apr", 10)
puts t

# More arguments can be passed.
t = Time.gm(2012, "jun", 30, 6, 30, 30, 50)
puts t

Output

2013-03-15 00:00:00 UTC
2010-04-10 00:00:00 -0700
2012-06-30 06:30:30 UTC

Leap. This method tells us if a year is a leap year or not. Leap years have an extra day. We must first create a Date object with the Date.new initialize method.

Note: For testing leap years, the day and month are not relevant. Just the year is needed.

Ruby program that uses leap method

require "date"

def days_in_year(year)
    d = Date.new(year, 1, 1)
    # See if the year is a leap year.
    if d.leap?
	return 366
    else
	return 365
    end
end

# Test years for leap status.
2000.upto(2010) do |year|
    puts year.to_s << " has " <<
	days_in_year(year).to_s << " days"
end

Output

2000 has 366 days
2001 has 365 days
2002 has 365 days
2003 has 365 days
2004 has 366 days
2005 has 365 days
2006 has 365 days
2007 has 365 days
2008 has 366 days
2009 has 365 days
2010 has 365 days

Upto, downto. Dates have helpful iterators. In Ruby we often prefer iterators over loops. For upto, the initial date is incremented upwards, a day at a time. And downto decrements the day.

Block: With iterators we specify a block that has a variable in it. With dates, this variable represents an interim day.

Iterators

Ruby program that uses upto, downto

require "date"

d1 = Date.new(2014, 10, 5)
d2 = Date.new(2014, 10, 7)

puts "upto"

# Iterate from low to high date.
d1.upto(d2) do |d|
    puts d
end

puts "downto"

# Iterate from high to low date.
d2.downto(d1) do |d|
    puts d
end

Output

upto
2014-10-05
2014-10-06
2014-10-07
downto
2014-10-07
2014-10-06
2014-10-05

Step. This iterator is more flexible than upto or downto. We specify the "increment" or decrement value. So a step of 7 advances an entire week on each iteration.

End: Step terminates when the next value reached has gone past the target value.

Also: Negative steps are allowed. With a negative step we can go backwards in time.

Ruby program that uses step

require "date"

first = Date.new(2014, 10, 1)
last = Date.new(2014, 11, 1)

# Advance seven days each iteration (these are Wednesdays).
first.step(last, 7) do |d|
    puts d
end

Output

2014-10-01
2014-10-08
2014-10-15
2014-10-22
2014-10-29

Next. The next and succ methods return the successive date—the "tomorrow" date. To me, the next() method is more clearly named. In this program, I specify the end date of October.

Here: These methods return the first day of November. Succ and next roll over from October to November.

Ruby that uses next, succ

require "date"

d = Date.new(2014, 10, 31)

# Get the next date with succ or next.
d2 = d.succ
puts d2

d2 = d.next
puts d2

Output

2014-11-01
2014-11-01

Months. We use shift operators with two greater than (or less than) signs to add (or subtract) months. This changes the month in a date. The plus and minus are used for days.

Ruby that adds, subtracts months

require "date"

d = Date.new(2015, 5, 1)

# Add two months to the date.
d2 = d >> 2
puts d2

# Subtract three months from the date.
d3 = d << 3
puts d3

Output

2015-07-01
2015-02-01

Wday. This number indicates the "day of week" or weekday of a date. It returns the numbers 0 through 6, with 0 meaning Sunday and 6 meaning Saturday.

And: When we call the next method the wday increments, unless it rolls over to 0 again.

Ruby that uses wday

require "date"

# This is a Sunday, so its number is 0.
d = Date.new(2014, 10, 5)
puts d.wday

# Next day is a Monday (number 1).
d = d.next
puts d.wday

# Tuesday (number 2).
d = d.next
puts d.wday

# One week later is Tuesday again.
d += 7
puts d.wday

Output

0
1
2
2

With DateTime, we access many date functions. These would be hard to implement. It is typically best to reuse these library methods where possible.

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