first and last char

[botp]

I always get tripped when working together w arrays and strings specially on,

string.first and string.last

of course, they err

wish there were #first and #last in String

just a thought
kind regards -botp

 

[Stefan Rusterholz]

irb(main):001:0> class String
irb(main):002:1> def first
irb(main):003:2> self.split('').first
irb(main):004:2> end
irb(main):005:1> def last
irb(main):006:2> self.split('').last
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):009:0> "testing".first
=> "t"
irb(main):010:0> "testing".last
=> "g"

Ew, that's awfully complex. You create n new objects from which you
throw n-1 away again...
Think of the memory! ;-)
def first; self[0,1]; end; def last; self[-1,1]; end

Regards
Stefan

 

[Daniel DeLorme]

Ew, that's awfully complex. You create n new objects from which you
throw n-1 away again...
Think of the memory! ;-)
def first; self[0,1]; end; def last; self[-1,1]; end

wrong, that's the first and last *bytes*, not characters.

def first; self[/\A./m]; end
def last; self[/.\z/m]; end
=> "語"

Daniel

 

[Stefan Rusterholz]

Ew, that's awfully complex. You create n new objects from which you
throw n-1 away again...
Think of the memory! ;-)
def first; self[0,1]; end; def last; self[-1,1]; end

wrong, that's the first and last *bytes*, not characters.

def first; self[/\A./m]; end
def last; self[/.\z/m]; end
=> "語"

Daniel

You are right, your solution is better.

Regards
Stefan

 

[Daniel DeLorme]

def first; self[/\A./m]; end
def last; self[/.\z/m]; end

$KCODE='u' => "u"
"日本語".first => "日"
"日本語".last

=> "語"

Daniel

You are right, your solution is better.

Only partly. Unfortunately, end-anchored regular expressions have pretty
abysmal performance.
=> 5.35788202285767

:-(
Daniel

 

[Trans]

Ew, that's awfully complex. You create n new objects from which you
throw n-1 away again...
Think of the memory! ;-)
def first; self[0,1]; end; def last; self[-1,1]; end

wrong, that's the first and last *bytes*, not characters.

For Ruby 1.9+ it will just be:

def first; self[0]; end; def last; self[-1]; end


my own version is (basically):

def first(pattern=//)
split(pattern).at(0)
end

which is a little more versatile. but I see the point about the
memory, and I'll add an optimization clause come 1.9.

T.

 

[Stefan Rusterholz]

Only partly. Unfortunately, end-anchored regular expressions have pretty
abysmal performance.

=> 5.35788202285767

:-(
Daniel

That can be helped. Assuming that there is no encoding with 1 char > 8
bytes:

def first; self[/\A./m]; end
def last; self[/.\z/m]; end
def last2; self[-8,8][/.\z/m]; end

Benchmark.measure{10000.times{str.first}}.real
=> 0.0643939971923828
Benchmark.measure{10000.times{str.last}}.real
=> 7.3151650428772
Benchmark.measure{10000.times{str.last2}}.real
=> 0.167464017868042

That's a 40x improvement for that string. For short strings it will
probably be slightly slower, but I'd say it's worth it.

Regards
Stefan

 

[Bertram Scharpf]

Hi,

Am Sonntag, 12. Aug 2007, 02:43:00 +0900 schrieb Felix Windt:

-----Original Message-----
From: botp [mailto:[email protected]]
Sent: Saturday, August 11, 2007 10:30 AM

wish there were #first and #last in String

irb(main):001:0> class String
irb(main):002:1> def first
irb(main):003:2> self.split('').first
irb(main):004:2> end
irb(main):005:1> def last
irb(main):006:2> self.split('').last
irb(main):007:2> end
irb(main):008:1> end
=> nil
irb(main):009:0> "testing".first
=> "t"
irb(main):010:0> "testing".last
=> "g"

Sometimes I wish every young programmer was forced to do a
month in Assembler and another one in C just to see what
cost in time and space some constructions cause.

Sorry, Felix!

Bertram

 

[Stephan Kämper]

Hi,

Am 13.08.2007 um 08:04 schrieb Bertram Scharpf:

Hi,

Am Sonntag, 12. Aug 2007, 02:43:00 +0900 schrieb Felix Windt:

-----Original Message-----
From: botp [mailto:[email protected]]
Sent: Saturday, August 11, 2007 10:30 AM

wish there were #first and #last in String

irb(main):001:0> class String
irb(main):002:1> def first
irb(main):003:2> self.split('').first
irb(main):004:2> end
irb(main):005:1> def last
irb(main):006:2> self.split('').last
irb(main):007:2> end
irb(main):008:1> end
=3D> nil
irb(main):009:0> "testing".first
=3D> "t"
irb(main):010:0> "testing".last
=3D> "g"

Sometimes I wish every young programmer was forced to do a
month in Assembler and another one in C just to see what
cost in time and space some constructions cause.

Sorry, Felix!

Well, here's something that should be a little bit less cycle =20
intensive (depending on how String#[](arg) is implemented):

class String
def last
self[-1].chr
end
end

Cheers


Stephan


--=20
Stephan K=E4mper/IT-Beratung http://www.stephankaemper.de
Softwaretest / Datenanalyse / Entwicklung

 

[Bertram Scharpf]

Hi,

Am Montag, 13. Aug 2007, 15:15:54 +0900 schrieb Stephan K=E4mper:

Am 13.08.2007 um 08:04 schrieb Bertram Scharpf:

Well, here's something that should be a little bit less cycle intensive= =20
(depending on how String#[](arg) is implemented):

class String
def last
self[-1].chr
end
end

This is what I would have implemented, too.

The difficult point is that it raises some questions:

- Should it return a Fixnum or a String of lenght 1?
- Should it be able to return UTF-8 characters?
- Should I define String#shift and String#pop now?

I don't recommend to discuss such question in an open forum
since I saw what happened to my String#notempty? proposal.

Bertram

--=20
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-scharpf.de

 

[Trans]

I don't recommend to discuss such question in an open forum
since I saw what happened to my String#notempty? proposal.

Sad for Ruby.

T.

 

[dblack]

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while the remaining parts are likely unreadable without MIME-aware tools.

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Hi --

Hi,

Am Montag, 13. Aug 2007, 15:15:54 +0900 schrieb Stephan K=E4mper:

Am 13.08.2007 um 08:04 schrieb Bertram Scharpf:

Well, here's something that should be a little bit less cycle intensive
(depending on how String#[](arg) is implemented):

class String
def last
self[-1].chr
end
end

This is what I would have implemented, too.

The difficult point is that it raises some questions:

- Should it return a Fixnum or a String of lenght 1?

If it ever gets added to Ruby, it will presumably be in 1.9/2.0, where
str[x] gives you a character anyway. If it doesn't get added, then
everyone will write their own, hopefully in a safe way, and can do
whatever they like

- Should it be able to return UTF-8 characters?
- Should I define String#shift and String#pop now?

There's already #chop. I don't know whether there are plans for
#lchop or equivalent.


David

--=20
* Books:
RAILS ROUTING (new! http://www.awprofessional.com/title/0321509242)
RUBY FOR RAILS (http://www.manning.com/black)
* Ruby/Rails training
& consulting: Ruby Power and Light, LLC (http://www.rubypal.com)
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