i have an array with numbers like this:
list1 = [50, 2, 99, 1, 958, 9, 6, 80]
and i need to compare all elements: digit by digit. for exemple, it will be important to compare "9", "99" and "958", because i'll need to put "99" at the end like this:
list1 = [1, 2, 50, 6, 80, 9, 958, 99]
Does Ruby has a function for this? thank you very much for your help :)
I think what you are looking for is this:
list1.sort_by(&:to_s)
So, this will lead to:
[50, 2, 99, 1, 958, 9, 6, 80].sort_by(&:to_s)
#=> [1, 2, 50, 6, 80, 9, 958, 99]
[50, 2, 1, 9].sort_by(&:to_s)
#=> [1, 2, 50, 9]
If you want reverse order, you can do:
[50, 2, 99, 1, 958, 9, 6, 80].sort_by(&:to_s).reverse
#=> [99, 958, 9, 80, 6, 50, 2, 1]
[50, 2, 1, 9].sort_by(&:to_s).reverse
#=> [9, 50, 2, 1]
And you can do .join to get the joined string:
[50, 2, 1, 9].sort_by(&:to_s).reverse.join
#=> "95021"
Try this: compare values converted to string, using String#<=> with Array#sort:
list1.sort { |a, b| a.to_s <=> b.to_s }
#=> [1, 2, 50, 6, 80, 9, 958, 99]
If I understand the question, even if the first three element of your output are confusing me about the logic.
<=> comparator assumes that the longer string is greater than the shorter string (when leading characters are the same). However, in this case, the shorter string should be considered greater. [10, 9, 95] is already sorted as per this logic, but 95910 is less than 99510.To extract just the first digit, you just need to map twice:
list = [50, 2, 99, 1, 958, 9, 6, 80]
p list.map(&:to_s).map { |n| n[0] }
# => ["5", "2", "9", "1", "9", "9", "6", "8"]
Update: The solution I've linked below is incorrect. The problem isn't as simple as it seemed.
Old answer follows:
However, the problem itself looked interesting, so I gave it a shot - i.e, to form the largest possible number from a list of numbers. However, I don't want to spoil the fun for you, so here's a link to a gist that solves the problem through normalization, in case you're interested.
list1.map(&:to_s).sortto convert to strings and that sorts it like what I think you're asking, but your 2nd example doesn't have the first half of your list sorted (e.g. why does 50 sort before 2?)