Re: 'first vs 'nth on maps
i've noticed a pattern in explanations in clojure that interface and runtime
are related. Is that the point being made here? Make expensive things hard
or at least explicit?
Maybe instead of nth, since that causes controversy,
call it "find-nth" or something?
On Wed, Apr 22, 2009 at 12:58 PM, Victor Rodriguez wrote:
>
> On Mon, Apr 20, 2009 at 5:17 PM, Hugh Winkler wrote:
> >
> > On Mon, Apr 20, 2009 at 1:59 PM, David Nolen
> wrote:
> >> Maps aren't ordered so this isn't a good idea anyway.
> >
> > It's a good idea if you have a sorted map. My example should have used
> > sorted-map.
> >
> >> The reason first/second work is because they call seq on the collection.
> >> (key (nth (seq {:a 1 :b 2 :c 3}) 1)) -> :b
> >>
> >
> > Thanks! I think 'nth ought to behave just like 'first and 'second,
> > don't you? If it's a good idea for 'first it's a good idea for 'nth.
>
> Probably not. I expect nth on a vector to be much faster than on a
> seq. O(1) vs O(n), respectively.
>
> Cheers,
>
> Victor Rodriguez.
>
> >
> > [Apologies to all for the several redundant posts on this topic. I've
> > been getting rejection messages from Google Groups for no reason].
> >
> >> On Mon, Apr 20, 2009 at 2:51 PM, hughw wrote:
> >>>
> >>> Hi all,
> >>>
> >>> Why should 'first and 'second work on maps, but not 'nth?
> >>>
> >>> user> (key (first {:a 1 :b 2 :c 3}))
> >>> :a
> >>> user> (key (nth {:a 1 :b 2 :c 3} 0))
> >>> ; Evaluation aborted.
> >>>
> >>> java.lang.UnsupportedOperationException: nth not supported on this
> >>> type: PersistentArrayMap (NO_SOURCE_FILE:0)
> >>> [Thrown class clojure.lang.Compiler$CompilerException]
> >>>
> >>> Thanks,
> >>> Hugh
> >>>
> >>>
> >>
> >>
> >> >
> >>
> >
> >
> >
> > --
> > Hugh Winkler, CEO
> > Wellstorm Development
> > 31900 Ranch Road 12
> > Suite 206
> > Dripping Springs, TX 78620
> > USA
> > http://www.wellstorm.com/
> > +1 512 264 3998 x801
> >
> > >
> >
>
> >
>
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Re: 'first vs 'nth on maps
On Mon, Apr 20, 2009 at 5:17 PM, Hugh Winkler wrote:
>
> On Mon, Apr 20, 2009 at 1:59 PM, David Nolen wrote:
>> Maps aren't ordered so this isn't a good idea anyway.
>
> It's a good idea if you have a sorted map. My example should have used
> sorted-map.
>
>> The reason first/second work is because they call seq on the collection.
>> (key (nth (seq {:a 1 :b 2 :c 3}) 1)) -> :b
>>
>
> Thanks! I think 'nth ought to behave just like 'first and 'second,
> don't you? If it's a good idea for 'first it's a good idea for 'nth.
Probably not. I expect nth on a vector to be much faster than on a
seq. O(1) vs O(n), respectively.
Cheers,
Victor Rodriguez.
>
> [Apologies to all for the several redundant posts on this topic. I've
> been getting rejection messages from Google Groups for no reason].
>
>> On Mon, Apr 20, 2009 at 2:51 PM, hughw wrote:
>>>
>>> Hi all,
>>>
>>> Why should 'first and 'second work on maps, but not 'nth?
>>>
>>> user> (key (first {:a 1 :b 2 :c 3}))
>>> :a
>>> user> (key (nth {:a 1 :b 2 :c 3} 0))
>>> ; Evaluation aborted.
>>>
>>> java.lang.UnsupportedOperationException: nth not supported on this
>>> type: PersistentArrayMap (NO_SOURCE_FILE:0)
>>> [Thrown class clojure.lang.Compiler$CompilerException]
>>>
>>> Thanks,
>>> Hugh
>>>
>>>
>>
>>
>> >
>>
>
>
>
> --
> Hugh Winkler, CEO
> Wellstorm Development
> 31900 Ranch Road 12
> Suite 206
> Dripping Springs, TX 78620
> USA
> http://www.wellstorm.com/
> +1 512 264 3998 x801
>
> >
>
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Re: 'first vs 'nth on maps
On Mon, Apr 20, 2009 at 5:17 PM, Hugh Winkler wrote > > > Thanks! I think 'nth ought to behave just like 'first and 'second, > don't you? If it's a good idea for 'first it's a good idea for 'nth. > It does seems like a reasonable behavior for sorted-set and sorted-map, but what else really? Also this does seem to imply a performance penalty (converting a large collection into a seq to which nth is applied). In anycase I don't know enough about the performance implications to say whether there's a reason for the current implementation of nth. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~--~~~~--~~--~--~---
Re: 'first vs 'nth on maps
On Mon, Apr 20, 2009 at 1:59 PM, David Nolen wrote:
> Maps aren't ordered so this isn't a good idea anyway.
It's a good idea if you have a sorted map. My example should have used
sorted-map.
> The reason first/second work is because they call seq on the collection.
> (key (nth (seq {:a 1 :b 2 :c 3}) 1)) -> :b
>
Thanks! I think 'nth ought to behave just like 'first and 'second,
don't you? If it's a good idea for 'first it's a good idea for 'nth.
[Apologies to all for the several redundant posts on this topic. I've
been getting rejection messages from Google Groups for no reason].
> On Mon, Apr 20, 2009 at 2:51 PM, hughw wrote:
>>
>> Hi all,
>>
>> Why should 'first and 'second work on maps, but not 'nth?
>>
>> user> (key (first {:a 1 :b 2 :c 3}))
>> :a
>> user> (key (nth {:a 1 :b 2 :c 3} 0))
>> ; Evaluation aborted.
>>
>> java.lang.UnsupportedOperationException: nth not supported on this
>> type: PersistentArrayMap (NO_SOURCE_FILE:0)
>> [Thrown class clojure.lang.Compiler$CompilerException]
>>
>> Thanks,
>> Hugh
>>
>>
>
>
> >
>
--
Hugh Winkler, CEO
Wellstorm Development
31900 Ranch Road 12
Suite 206
Dripping Springs, TX 78620
USA
http://www.wellstorm.com/
+1 512 264 3998 x801
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Re: 'first vs 'nth on maps
Maps aren't ordered so this isn't a good idea anyway.
The reason first/second work is because they call seq on the collection.
(key (nth (seq {:a 1 :b 2 :c 3}) 1)) -> :b
On Mon, Apr 20, 2009 at 2:51 PM, hughw wrote:
>
> Hi all,
>
> Why should 'first and 'second work on maps, but not 'nth?
>
> user> (key (first {:a 1 :b 2 :c 3}))
> :a
> user> (key (nth {:a 1 :b 2 :c 3} 0))
> ; Evaluation aborted.
>
> java.lang.UnsupportedOperationException: nth not supported on this
> type: PersistentArrayMap (NO_SOURCE_FILE:0)
> [Thrown class clojure.lang.Compiler$CompilerException]
>
> Thanks,
> Hugh
>
> >
>
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