From: "Peña, Botp" <botp@...>
Date: 2007-06-28T19:43:00+09:00
Subject: Re: Array Problem, sort Array

From: F. Senault [mailto:fred@lacave.net] :
# Le 28 juin � 06:17, Pe�a, Botp a �crit :
# > solution: a) convert elements to some common class (string 
# is common)
# >           b) filter those you don't want sorted (using 
# compact/reject/..)
# >              or select those you want (using select/map/..)
# 
# c) Use a sort(_by) block (maybe that's what you meant in a) :
# >> ["a", nil, "b"].sort_by { |e| (e.nil? ? 'z' : e) }
# => ["a", "b", nil]

yap, they're all the same, string comparison.

another stupid sample below. the comparison is in integers, indirectly handled by  array#index.

shelf_order  = [nil, "orange","spices","apple","peaches", "herbs"]
tobe_ordered = ["herbs", "orange","apple",nil,"peaches"]
tobe_ordered.sort_by  do |e| 
   shelf_order.index(e)
end
=> [nil, "orange", "apple", "peaches", "herbs"]

 
# > A little digression for everyone though...
# >   irb(main):013:0> [nil].sort
# >   => [nil]
# >
# > is that intended?
# 
# Well, you don't need the comparison operator where there's only one
# element, do you ?

careful with the "one" there. The array returned may be complex.
eg,
irb(main):029:0> [[nil,[nil,"a"]]].sort
=> [[nil, [nil, "a"]]]
irb(main):030:0> [[nil,[nil,"a"]]].flatten.sort
NoMethodError: undefined method `<=>' for nil:NilClass
        from (irb):30:in `sort'

again, as i've said to Phrogz, the behavior hints that nil elements by themselves are sortable. Remember, programs contain blackboxes wc may be complex and not obvious, eg
   complex_proc_ret_array.sort_complex.foo_proc.bar_proc

one could argue bluntly too, eg
[nil].sort
=>[nil]      # yes, there is no need to sort
[nil,nil].sort
=>[nil,nil]  # yes, there is no need to sort

I really value consistency of object behavior when it comes to ruby, maybe because it's too dynamic and i want least number of surprises (especially when you chain things).

Anyway, I've overlooked this behavior and now I'll have to recheck again my testcases ;)

thanks Senault and Phrogz, and kind regards -botp