Ruby custom string sort

Question

Input string:

1654AaBcDddeeFF

Output string:

1456acddeeABDFF

Code I tried:

test_array = []
'1654AaBcDddeeFF'.each_byte do |char|
  test_array << char
end

test_array.sort.pack('C*')
# => 1456ABDFFacddee

But I would like to see the upper case characters at last.

@ChaseGilliam not to be a nazi but "overloading" is not a ruby convention or even possible. Jörg W Mittag Wrote an excellent post explaining this concept. Also Array#sort will allow you to specify any custom sorting you want — engineersmnky
– engineersmnky, Commented Apr 22, 2015 at 21:01
@engineersmnky ok, you are correct. You can however def <=> ... end and yeah, Array#sort is a better approach. — Chase
– Chase, Commented Apr 22, 2015 at 21:27

hirolau · Accepted Answer · 2015-04-23 07:01:34Z

13

What about this?

p '1654AaBcDddeeFF'.each_char.sort_by(&:swapcase).join #=> "1456acddeeABDFF"

Edit: As @Cary Swoveland pointed out .chars is just a shortcut for .each_char.to_a and since we do not need to to_a here .each_char is a better method to use

edited Apr 23, 2015 at 7:01

answered Apr 22, 2015 at 20:56

hirolau

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3 Comments

Appunu Over a year ago

Thats a very sneaky answer. Loved the approach though. Thanks a lot

Cary Swoveland Over a year ago

Nice one. Maybe each_char rather than chars to avoid the creation of a temporary array.

Mark Thomas Over a year ago

Had to think about this one for a while. Very clever.

michael_wu · Accepted Answer · 2015-04-23 12:26:10Z

5

Since @hirolau's already taken swapcase, I offered an alternative (even though I prefer his answer). Alas, @Stefan identified a flaw, but suggested a nice fix:

str = '1654AaBcDddeeFF'

order_array = [*'0'..'9',*'a'..'z',*'A'..'Z']
str.each_char.sort_by { |c| order_array.index(c) }.join
  #=> "1456acdeABDF"

(I am a mere scribe.)

One advantage of this approach is that you could use it for other orderings. For example, if:

str = '16?54!AaBcDdde,eFF'

and you also wanted to group the characters `'!?,' at the beginning, in that order, you could write:

order_array = [*'!?,'.chars,*'0'..'9',*'a'..'z',*'A'..'Z']
str.each_char.sort_by { |c| order_array.index(c) }.join
  #=> "!?,1456acdeABDF"

We can make this a bit more efficient by converting order_array to a hash. For the last example:

order_hash = Hash[order_array.each_with_index.to_a]

then:

str.each_char.sort_by { |c| order_hash[c] }.join
  # => "!?,1456acddeeABDFF"

edited Apr 23, 2015 at 12:26

michael_wu

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answered Apr 22, 2015 at 21:49

Cary Swoveland

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5 Comments

Stefan Over a year ago

Note that this removes duplicate characters.

Stefan Over a year ago

You could use an order array and sort_by { |c| order.index(c) }

Appunu Over a year ago

Looks nice. But is actual sorting happening here ? Like say are they sorted based on ASCII values when it comes to special characters ? To me it looks like mere grouping when it comes to symbols but am not sure, please enlighten me

Cary Swoveland Over a year ago

@Appunu, you'd have to include the special characters in order_array. For example, if str = 'βΔ3Rαe' and we want to modify my example to put the Greek letters at the end (lower then upper case), we would need order_array = [*'0'..'9',*'a'..'z',*'A'..'Z',*'α'..'ω',*'Α'..'Ω'], str.each_char.sort_by { |c| order_array.index(c) }.join #=> "3eRαβΔ". Note also str.each_char.map(&:swapcase).join #=> "βΔ3rαE".

Appunu Over a year ago

Eventhough I accepted the previous answer. This solution provided by @CarySwoveland is the optimal one under various situations where we need to involve special characters and symbols.

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