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comp.lang.ruby

Re: iteration the ruby way

e

2/6/2005 7:12:00 PM

> Lähettäjä: "Robert Klemme" <bob.news@gmx.net>
> Aihe: Re: iteration the ruby way
>
>
> "E S" <eero.saynatkari@kolumbus.fi> schrieb im Newsbeitrag
> news:20050206143902.PIMQ15813.fep31-app.kolumbus.fi@mta.imail.kolumbus.fi...
> >> Lähettäjä: Kaspar Schiess <eule@space.ch>
> >> Aihe: Re: iteration the ruby way
> >>(In response to news:1107566961.943586.81760@g14g2000cwa.googlegroups.com
> > by William James)
> >>> Shouldn't that be
> >>>
> >>> ary[0...-1].each {|e| do_something(e) }
> >>> do_something_else(ary.last)
> >>>
> >>> or
> >>>
> >>> ary[0..-2].each {|e| do_something(e) }
> >>> do_something_else(ary.last)
> >>>
> >>> ?
> >>
> >>I would prefer this solution for its clarity of expression.
> >
> > Me too :) I just think the #inject won on the neat-o factor,
> > particularly since it seemed adequate for the OP.
>
> Partly yes and partly no: apart from the cute factor, there is a real
> advantage of the inject solutions show: they work for *all* Enumerables
> while the array indexing works only for arrays. So #inject is more general.
> Also, Array#[] creates a new array instance along the way which is a bit
> inefficient. But I do agree that the indexing might be more readable.

I think assuming an Array is valid in the described scenario (which
is the last element in a Hash, after all?) #inject certainly works
for the OP's scenario, but if the goal is to apply a different method
on the last element or even just to detect the last element, it is not
as intuitive as indexing or an explicit #last. In addition, #each and
#map provide different semantics for further clarity.

> Kind regards
>
> robert

E
>



4 Answers

dblack

2/6/2005 9:00:00 PM

0

Robert Klemme

2/7/2005 7:52:00 PM

0


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.61.0502061257450.13178@wobblini...
Hi --

On Mon, 7 Feb 2005, E S wrote:

>> "Robert Klemme" <bob.news@gmx.net>
>> Aihe: Re: iteration the ruby way
>>
>>
>> "E S" <eero.saynatkari@kolumbus.fi> schrieb im Newsbeitrag
>> news:20050206143902.PIMQ15813.fep31-app.kolumbus.fi@mta.imail.kolumbus.fi...
>>>> Lähettäjä: Kaspar Schiess <eule@space.ch>
>>>> Aihe: Re: iteration the ruby way
>>>> (In response to
>>>> news:1107566961.943586.81760@g14g2000cwa.googlegroups.com
>>> by William James)
>>>>> Shouldn't that be
>>>>>
>>>>> ary[0...-1].each {|e| do_something(e) }
>>>>> do_something_else(ary.last)
>>>>>
>>>>> or
>>>>>
>>>>> ary[0..-2].each {|e| do_something(e) }
>>>>> do_something_else(ary.last)
>>>>>
>>>>> ?
>>>>
>>>> I would prefer this solution for its clarity of expression.
>>>
>>> Me too :) I just think the #inject won on the neat-o factor,
>>> particularly since it seemed adequate for the OP.
>>
>> Partly yes and partly no: apart from the cute factor, there is a real
>> advantage of the inject solutions show: they work for *all* Enumerables
>> while the array indexing works only for arrays. So #inject is more
>> general.
>> Also, Array#[] creates a new array instance along the way which is a bit
>> inefficient. But I do agree that the indexing might be more readable.
>
> I think assuming an Array is valid in the described scenario (which
> is the last element in a Hash, after all?)

> If you goal was to create a string representation of the hash, with
> some kind of marker between each key/value pair -- but not after the
> last one -- then the last-ness of the last element would be important
> in the sense that you'd treat it differently (whatever it was, and
> whether or not it remained the same from one run to another).

Note though that you might as well treat the *first* element specially.
IMHO that's usually easier even with #each:

first = true
enum.each do |e|
if first
first = false
else
print " -- "
end
print e
end
print "\n"


Kind regards

robert

Martin DeMello

2/8/2005 4:30:00 AM

0

Robert Klemme <bob.news@gmx.net> wrote:
>
> Note though that you might as well treat the *first* element specially.
> IMHO that's usually easier even with #each:
>
> first = true
> enum.each do |e|
> if first
> first = false
> else
> print " -- "
> end
> print e
> end
> print "\n"

Though I hate doing this, because that 'if', that you know is going to be
useless after the first time, is nonetheless run for every subsequent
element. I guess in terms of actually running time it's negligible, but
it still feels ugly.

martin

Robert Klemme

2/8/2005 8:50:00 AM

0


"Martin DeMello" <martindemello@yahoo.com> schrieb im Newsbeitrag
news:jfXNd.318521$6l.10705@pd7tw2no...
> Robert Klemme <bob.news@gmx.net> wrote:
> >
> > Note though that you might as well treat the *first* element
specially.
> > IMHO that's usually easier even with #each:
> >
> > first = true
> > enum.each do |e|
> > if first
> > first = false
> > else
> > print " -- "
> > end
> > print e
> > end
> > print "\n"
>
> Though I hate doing this, because that 'if', that you know is going to
be
> useless after the first time, is nonetheless run for every subsequent
> element. I guess in terms of actually running time it's negligible, but
> it still feels ugly.

Yes, totally agree. I just wanted to show a more readable solution than
the #inject variants to show that treating the first element specially
might be easier or at least as easy as treating the last element
specially.

Kind regards

robert