Here are two range values.
('1'..'10').to_a => ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
but,
('2'..'10').to_a => []
Why does the second one return an empty array in ruby 1.8.7?
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4 Answers
The issue is that Ruby 1.8 is trying to determine whether ('2'..'10') is a valid range as part of its analysis of the code, and deciding that it's invalid. '2' sorts after '10' making the range values backwards.
This is a common problem when people try to sort string values, and they'll encounter it again and again until they learn that trick never works.
Using 1.8.7:
('2'..'10').to_a
=> []
('02'..'10').to_a
=> ["02", "03", "04", "05", "06", "07", "08", "09", "10"]
Or:
(2..10).map(&:to_s)
=> ["2", "3", "4", "5", "6", "7", "8", "9", "10"]
I'd probably use the last method if I needed compatibility with 1.8 and 1.9+ Rubies.
Comments
irb(main):001:0> '2' > '10'
=> true
irb(main):002:0> '1'>'10'
=> false
Because of the string comparison algorithm, range cannot be created with lower bound bigger than the upper bound.
ACTUALLY it works in 1.9.3. Strange.
3 Comments
Inaccessible
couldn't get "range cannot be created with lower bound bigger than the upper bound". can you explain me little bit?
Anton
Well, Range object is created using two objects as in
(1..5), 1 is the lower bound and 5 is an upper bound. Range class uses succ method on lower bound until it reaches the upper bound. succ method in string returns '10' after '9' in 1.9.3, which does not seem logical to me personally.Anton
succ returns next element in an implied sequence. You don't expect that 5.succ == 4, do you? That is why (5..1).to_a == []. Hope you get the idea.That's not what I'm getting:
irb(main):001:0> ('2'..'10').to_a
=> ["2", "3", "4", "5", "6", "7", "8", "9", "10"]
Unrelated to the question, though: the correct way is:
(2..10).to_a
(I am using Ruby 1.9.3)
1 Comment
Tom L
If you're stuck using 1.8.7 why not just convert the values to integers?
('2'.to_i..'10'.to_i).to_ain ruby2.0.0-p-0 this is what I am getting :
["2", "3", "4", "5", "6", "7", "8", "9", "10"]
