Re: collection enumeration

Bert Freudenberg wrote:
> Am 23.08.2006 um 21:15 schrieb cdrick:
>
> > Hi all -
> >
> > not an important question here, more a discussion. I was wondering
> > which method is the more appropriate (nice and/or efficient) to
> > enumerate all the elements of a collection and the index of each
> > elements...
> >
> >
> > (a) ---- à la C
> >
> > (1 to: collection size) do: [:index |
> >                         html render: 'Victime ', index printString.
> >                                                html render:
> > collection at: index]
> >
> > (b) --- indexOf
> >
> > collection do: [:victim |
> >                         html render: 'Victime ', (collection indexOf: 
> > victim) printString.
> >                                                html render: victim]
> >
> > (c) ---- keysAndValuesDo:
> >
> > collection keysAndValuesDo: [:index :victim |
> >                         html render: index printString.
> >                                                html render: member]
> >
> > (d) ---- using a local var
> >
> > | index |
> > index := 0.
> > collection do: [:victim | index := index + 1.
> >                         html render: 'Victime ', index printString.
> >                                                html render: victim]
> >
> > What solution would you suggest ?
> > I think we forget (a) and (d)
> > I like (c) but maybe (b) is more readable ?
> >
> > Maybe there is another way ?
>
> (c), though I like #withIndexDo: better since it mimics the #with:do: 
> pattern.

I would vote for #withIndexDo: too which has in 'intention revealing 
name' :-)

And, please forget about (b), this is way too slow and wrong.

Slow because the complexity jump from O(n) to O(n²). Remember that 
#indexOf: has to search for the element in all the collection.

Wrong because:

collection := #($a $b $a).
collection
  do: [:each | Transcript
                 show: (collection indexOf: each);
                 space]

Will print '1 2 1' instead of '1 2 3'. Index answered by #indexOf: if 
the first index on which the object is found.


Bye