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comp.lang.ruby

Error in Ruby text comparison?

Greg Willits

10/27/2007 11:13:00 AM

'1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'

Wouldn't you think that is supposed to be TRUE ?

All my text editors and Excel and Numbers all sort it so that 1s...
comes before 1X...

But Ruby says the above comparison is false.

What am I missing?

-- gw
--
Posted via http://www.ruby-....
7 Answers

Greg Willits

10/27/2007 11:27:00 AM

0

Greg Willits wrote:
> '1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'
>
> Wouldn't you think that is supposed to be TRUE ?
>
> All my text editors and Excel and Numbers all sort it so that 1s...
> comes before 1X...
>
> But Ruby says the above comparison is false.
>
> What am I missing?

Strange, this list:

s, S, s, a, B

in Excel, Numbers, and in Araelium Edit comes out as this when sorted

a, B, s, S, s

TextWrangler puts them as

a, B, s, s, S

Ruby sorts ['s','S','s','a','B'].sort as

["B", "S", "a", "s", "s"]

MySQL (as I have it set up) sorts like the OS X apps.

Trying to do a binary search with a ruby array based on text sorted by
something else is getting hosed.

Oh... duh, have Ruby sort it :-P

Could get very expensive, but I guess I'll have to do it.

-- gw

--
Posted via http://www.ruby-....

Arlen Cuss

10/27/2007 12:35:00 PM

0


On Sat, 2007-10-27 at 20:27 +0900, Greg Willits wrote:
> Greg Willits wrote:
> > '1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'
> >
> > Wouldn't you think that is supposed to be TRUE ?
> Strange, this list:
>
> s, S, s, a, B
>
> in Excel, Numbers, and in Araelium Edit comes out as this when sorted
>
> a, B, s, S, s
>
> TextWrangler puts them as
>
> a, B, s, s, S
>
> Ruby sorts ['s','S','s','a','B'].sort as
>
> ["B", "S", "a", "s", "s"]

irb to the rescue:
irb(main):001:0> 'a' < 'b'
=> true
irb(main):002:0> "A" < 'b'
=> true
irb(main):003:0> "a" < "B"
=> false
irb(main):004:0> ?a < ?b
=> true
irb(main):005:0> ?A < ?b
=> true
irb(main):006:0> ?a < ?B
=> false
irb(main):007:0> ?A
=> 65
irb(main):008:0> ?a
=> 97
irb(main):009:0>

Ruby's sorting these strings by ASCII order, and as you can see here, capital letters come first! So "A" is always less than 'a', etc.

Arlen

Eustaquio 'TaQ' Rangel

10/27/2007 12:53:00 PM

0

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Hash: SHA1

Hi!

> Ruby's sorting these strings by ASCII order, and as you can see here, capital letters come first! So "A" is always less than 'a', etc.

This is because Ruby follow the lexicographical order for sorting. If you need
case-insensitive comparisons, you can change the way the sorting works with:

puts '1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'
puts 'a' < 'B'

class String
alias <=> casecmp
end

puts '1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'
puts 'a' < 'B'

Let's see what ri tell us about casecmp:

ri casecmp
- --------------------------------------------------------- String#casecmp
str.casecmp(other_str) => -1, 0, +1
- ------------------------------------------------------------------------
Case-insensitive version of String#<=>.

"abcdef".casecmp("abcde") #=> 1
"aBcDeF".casecmp("abcdef") #=> 0
"abcdef".casecmp("abcdefg") #=> -1
"abcdef".casecmp("ABCDEF") #=> 0

Best regards,

- --
Eustáquio "TaQ" Rangel
http://eustaquio...

"When someone says, 'I want a programming language in which I need only say what
I want done,' give him a lollipop."
Alan Perlis


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Nobuyoshi Nakada

10/27/2007 12:54:00 PM

0

Hi,

At Sat, 27 Oct 2007 20:13:28 +0900,
Greg Willits wrote in [ruby-talk:276099]:
> '1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'
>
> Wouldn't you think that is supposed to be TRUE ?

No.

> But Ruby says the above comparison is false.

'1sqHmb5b8G9mN'.casecmp('1Xv5LeB9bMdar') < 0

returns true.

--
Nobu Nakada

Wolfgang Nádasi-donner

10/27/2007 3:25:00 PM

0

Greg Willits wrote:
> '1sqHmb5b8G9mN' < '1Xv5LeB9bMdar'
>
> Wouldn't you think that is supposed to be TRUE ?
>
> All my text editors and Excel and Numbers all sort it so that 1s...
> comes before 1X...
>
> But Ruby says the above comparison is false.
>
> What am I missing?
>
> -- gw

Ruby - like several other languages - makes the comparison based on the
underlying code. When you only have English texts it may be confusing,
because you expect a different behavior.

I think it is always a bad idea to compare texts in this way, because
the character sequence is first based on language definitions (e.g.
letter "ö" is in German the same lake "oe", while in Swedish it comes
after "z"), and second for a language there may be different standards
too (e.g. telefone book sequence versus language definition sequence, as
in German).

If You want to compare Strings based on the usage in a language, you
should better use an appropriate sequence definition.

Wolfgang Nádasi-Donner
--
Posted via http://www.ruby-....

Daniel Brumbaugh Keeney

10/27/2007 10:14:00 PM

0

On 10/27/07, Wolfgang Nádasi-Donner <ed.odanow@wonado.de> wrote:> If You want to compare Strings based on the usage in a language, you> should better use an appropriate sequence definition.What is the best way to create a new sort order?For example, if the order is this:%w[1 2 3 4 5 6 7 8 9 0 A a B b...]and every other character to be sorted using Array#sort after thealphanumeric characters.-------------------------------------------Daniel Brumbaugh KeeneyDevi Web DevelopmentDevi.WebMaster@gMail.com-------------------------------------------

Daniel Brumbaugh Keeney

10/27/2007 10:16:00 PM

0

On 10/27/07, Devi Web Development <devi.webmaster@gmail.com> wrote:
> For example, if the order is this:

Mind you, that was just a sample, I really want to understand the best
method to make any arbitrary sort order.

-------------------------------------------
Daniel Brumbaugh Keeney
Devi Web Development
Devi.WebMaster@gMail.com
-------------------------------------------