Ranges with dates (in Groovy) at log4p

Ranges with dates (in Groovy)

Published by peter December 1st, 2007 in groovy.

During my previous ramblings with Groovy I didn't touch anything fancy in the Date/Calendar API; no need for it. But after reading a lengthy blogpost on the topic I just needed to have a look at it.

Consider the following code:

PLAIN TEXT

GROOVY:

sdf = new java.text.SimpleDateFormat("dd-MM-yyyy")
bd_daan = sdf.parse("23-01-1980")
bd_peter = sdf.parse("18-01-1979")
t = Calendar.instance
all_sundays = (bd_peter..bd_daan).findAll{
t.time = it;
t.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY
}
all_sundays.each{
println sdf.format(it)
}

It prints a list of all Sundays between my and my wifes' birthday. Most of the 'magic' is done by the range operator (..) on which one can call all collection operations.

I somehow expected a more groovy like interface to the Calendar object; t.get( xxx ) just doesn't feel Groovy. Might be a nice little project to use method missing to make calls like t.dayOfWeek to work... maybe tomorrow

9 Responses to “Ranges with dates (in Groovy)”

Feed for this Entry Trackback Address

1 railsguru Dec 2nd, 2007 at 1:04 pm

bd_daan = Date.parse("23-01-1980")
bd_peter = Date.parse("18-01-1979")

(bd_peter..bd_daan).each { |d| puts d if d.wday.zero? }

2 peter Dec 2nd, 2007 at 8:08 pm

If you execute the code exactly as you pasted it; it wouldn't work. The Groovy code does work without any further 'import' or 'require'.

If I execute:


irb> require 'date/format'
irb> bd_peter = Date._parse('18-01-1979')
=> {:mon=>1, :year=>1979, :mday=>18}
irb> bd_peter = Date._parse('18-01-1979')
=> {:mon=>1, :year=>1979, :mday=>18}
irb> bd_daan = Date._parse('23-01-1980')
=> {:mon=>1, :year=>1980, :mday=>23}
irb> (bd_peter..bd_daan).each{|d| puts d if d.wday.zero?}
ArgumentError: bad value for range
        from (irb):18
        from :0

Did I import the wrong date??

There also is a slight difference in your ruby solution; which I could have used in my example... I build an array of the results and display it in a second each loop... could have been simpler:


sdf = new java.text.SimpleDateFormat("dd-MM-yyyy")

bd_daan = sdf.parse("23-01-1980")
bd_peter = sdf.parse("18-01-1979") 

t = Calendar.instance
all_sundays = (bd_peter..bd_daan).each{
	t.time = it;
	if(t.get(Calendar.DAY_OF_WEEK) == Calendar.SUNDAY)
		println sdf.format(it)
}

Mind you, the use of a intermediate Calendar object is a bit overkill in this case... as is the use of the full blown Java date formatter. But the advantage is: full locale awareness when needed.

3 railsguru Dec 2nd, 2007 at 9:41 pm

The code is mend to be run in a Rails environment e.g. script/console. Anyway.. not trying to prove a point, just checked to see if the same could be done in Ruby
4 peter Dec 2nd, 2007 at 9:46 pm

Aha, makes sense ... I always tend to forget about the fact that Rails uses its' own date and time classes...
5 peter Dec 2nd, 2007 at 9:48 pm

But hey, interesting... Rails' date object can actually be used in a range?
6 railsguru Dec 2nd, 2007 at 9:57 pm

Indeed! That's the new thing I learned from this small excercise
As long as your class implements and succ you can use it in Range:

http://ruby-doc.org/core/classes/Range.html
7 railsguru Dec 2nd, 2007 at 9:58 pm

Grr, <=> and succ that is..
8 peter Dec 3rd, 2007 at 11:19 am
With a little help from a colleague if figured out how to used Rails' date and time extensions when not running in Rails. Just load active_support:
```
irb(main):005:0> require 'rubygems'
=> true
irb(main):006:0> require 'active_support'
=> true
```