在什麼語言都要『炒』好幾次？
(1..10).to_a
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
(10..1).to_a
=> []
所以
for i in 1..10 do puts i end
會印 1 到 10
for i in 10..1 do puts i end
卻不會印 10 到 1
雖然可以用 10.downto(1)
不過還是太 Orz 了….
或許 Python 更適合你。
Python:
for i in reversed(xrange(1,11)):
print i
這學期有個 project 有點想用 Ruby on Rails 做
如果 Python 的話也許可以用 http://www.djangoproject.com/
不過有辦法學那麼多嗎…. Orz
Please check the ruby-talk: 8993 and 39342
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/8993
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/39342
And be aware of Range using on Array index:
For example:
ary = %w[a b c d e]
ary[1..-1] # => [‘b’, ‘c’, ‘d’, ‘e’]
If we *assume* Range support from “big” to “small”,
the example 1..-1 will like have 1, 0, -1 elements
and ary[1..-1] will returns [‘b’, ‘a’, ‘e’]
but the current design is not like this way …
The main raison Range do not support from “big” to “small” is
because the Range is define base on object’s “succ”( or alias “next”) and “”
BTW: You could “redefine” the Range to behaviour as you like.
“succ” and ” < = > ”
後面是 *宇宙飛碟* operator.
Not prefect at all ( need to take care of === also, string Range … etc),
but it seems to work for what you expect.
class Range
alias old_each each
def each(&block)
return old_each(&block) unless first > last
first.downto(last) { |e| yield e }
return self
end
end
p (1..10).to_a
p (10..1).to_a
(10..1).each { |e| p e }
也許它可以加個 pred 或 prev, 再把用在 array 的情形改一下, 功能上會更對稱一點….
我好像 柯南 – 引爆摩天樓 裡那個超執著對稱的森谷帝二教授…. XD
可以用 range(1, 11)[::-1] 或是 xrange(10, 0, -1)。
我想搭紅寶石列車，Duncan 集團誘惑我乘巨蟒….
這幾天在看 Programming Ruby (2nd. Ed.)
看到 Array 部分時，好奇試了這些個東西
a = ["a", "b", "c", "d", "e"] a[3, -2] a[3..1] a[-1..1] a[-1..-3]
結果
a[3, -2] => nil a[3..1] => [] a[-1..1] => [] a[-1..-3] => []
我想要是我來設計，大概會給它弄成這樣
a[3, -2] => ["d", "c"] a[3..1] => ["d", "c", "b"] a[-1..1] => ["e", "d", "c", "b"] a[-1..-3] => ["e", "d", "c"]
因為既然負的 index 是由最後往前數（a[-1] => “e”），我會覺得取好幾個也要有由後往前取的功能 😛
Welcome to the Ruby World.
The [] rule is also apply to []=
So, if a = [‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
and if a[3..1] => [‘d’, ‘c’, ‘b’]
What you would like to see if you write something like
a[3..1] = [1, 2, 3, 4] ?
a will become to [‘a’, 4, 3, 2, 1, ‘e’] ?
One good thing about Ruby is everything are open.
Even the core library.
There are also calibre and facets project to change the array index to the way they like.
I can easily change the length negative value behavior as you like ( the Range one, leave to yourself to do it) , for example :
class Array
alias_method :old, :"[]"
def [](*args) # define my new [] method for Array
begin
old(*args) unless args.length == 2 && args.last < 0
(0...-args.last).inject([]) { |a, i| a << self.slice(args.first - i) }
rescue
old(*args)
end
end
end
a = %w[a b c d e] #=> a = ['a', 'b', 'c', 'd', 'e']
a[3, -2] #=> ['d', 'c']
So, if you don’t like the default way, change to what you like.
On Ruby, you could even change 1+1 to become 3 if you like. 🙂
Yes, I will let a be [‘a’, 4, 3, 2, 1, ‘e’] after a[3..1] = [1, 2, 3, 4].
And I finished the homework, but only [] not []=.
class Array
alias_method :old, :"[]"
def [](*args) # define my new [] method for Array
begin
if (args.length == 2 && args.last < 0)
(0...-args.last).inject([]) { |a, i| a << self.slice(args.first - i) }
elsif (args.length == 1 && args.first.class == Range)
range = args.first
first = range.first < 0 ? range.first + self.length : range.first
last = range.last < 0 ? range.last + self.length : range.last
if (first > last)
length = (first - last).abs
length += 1 unless range.exclude_end?
(0...length).inject([]) { |a, i| a << self.slice(range.first - i) }
else
old(*args)
end
else
old(*args)
end
rescue
old(*args)
end
end
end
a = %w[a b c d e]
a[-1..-3] #=> ["e", "d", "c"]
a[-1...-3] #=> ["e", "d"]
a[-1..1] #=> ["e", "d", "c", "b"]
a[-1...1] #=> ["e", "d", "c"]
a[4..2] #=> ["e", "d", "c"]
a[4...2] #=> ["e", "d"]
Ooops, I found my bug …
The line
old(*args) unless args.length == 2 && args.last < 0
should be like
return old(*args) unless args.length == 2 && args.last < 0