Hello,

When traversing an ArrayList which is faster?

For Each oItem as Something in me.ArrayList
.....
.....
Next

OR

Dim oItem as Something
Dim Enumerator as IEnumerator = me.ArrayList.GetEnumerator()

While Enumerator.MoveNext()
...
...
End While

Thanks,
Rob Panosh

"Rob Panosh" <rob_!!!NO!!!SPAM!!!_(E-Mail Removed)>
schrieb
> Hello,
>
> When traversing an ArrayList which is faster?
>
> For Each oItem as Something in me.ArrayList
> ....
> ....
> Next
>
> OR
>
> Dim oItem as Something
> Dim Enumerator as IEnumerator = me.ArrayList.GetEnumerator()
>
> While Enumerator.MoveNext()
> ...
> ...
> End While

Both versions are equal. For Each also uses the IEnumerator interface.


--
Armin

I think you will feel no difference other than a beautiful code with the
first option.

The For Each statement also uses the IEnumerator interface, but it
simplifies the use for you.





-----------

Rafael Pivato



"Rob Panosh" <rob_!!!NO!!!SPAM!!!_(E-Mail Removed)> escreveu na
mensagem news:(E-Mail Removed)...
> Hello,
>
> When traversing an ArrayList which is faster?
>
> For Each oItem as Something in me.ArrayList
> ....
> ....
> Next
>
> OR
>
> Dim oItem as Something
> Dim Enumerator as IEnumerator = me.ArrayList.GetEnumerator()
>
> While Enumerator.MoveNext()
> ...
> ...
> End While
>
> Thanks,
> Rob Panosh
>
>
>
>
>
>

Thanks ...

"Armin Zingler" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> "Rob Panosh" <rob_!!!NO!!!SPAM!!!_(E-Mail Removed)>
> schrieb
> > Hello,
> >
> > When traversing an ArrayList which is faster?
> >
> > For Each oItem as Something in me.ArrayList
> > ....
> > ....
> > Next
> >
> > OR
> >
> > Dim oItem as Something
> > Dim Enumerator as IEnumerator = me.ArrayList.GetEnumerator()
> >
> > While Enumerator.MoveNext()
> > ...
> > ...
> > End While
>
> Both versions are equal. For Each also uses the IEnumerator interface.
>
>
> --
> Armin
>

Thanks ...

"Rafael Pivato" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I think you will feel no difference other than a beautiful code with the
> first option.
>
> The For Each statement also uses the IEnumerator interface, but it
> simplifies the use for you.
>
>
>
>
>
> -----------
>
> Rafael Pivato
>
>
>
> "Rob Panosh" <rob_!!!NO!!!SPAM!!!_(E-Mail Removed)> escreveu na
> mensagem news:(E-Mail Removed)...
> > Hello,
> >
> > When traversing an ArrayList which is faster?
> >
> > For Each oItem as Something in me.ArrayList
> > ....
> > ....
> > Next
> >
> > OR
> >
> > Dim oItem as Something
> > Dim Enumerator as IEnumerator = me.ArrayList.GetEnumerator()
> >
> > While Enumerator.MoveNext()
> > ...
> > ...
> > End While
> >
> > Thanks,
> > Rob Panosh
> >
> >
> >
> >
> >
> >
>
>

Hi Rob,

For Each uses an enumerator behind the scenes so, as expected, on the
tests that I did, they came out even (to the 3rd dec place). The difference is
almost certainly due to timng inaccuracies.

On the other hand - using For I = 0 To al.Count - 1 was three times
faster!

Regards,
Fergus

Yep, nice post....

And the reason for it is simple:
you will naturally have fast For
statements using integers
(no method calls) and to get
the element you just have
to do one call for each iteration.

Using the enumerator you
do some abstracts, but you
pay for it, calling one method
just to verify if it is the end.

But IEnumerator still having
various advantages... (maybe
not performance like)

---
Rafael Pivato


"Fergus Cooney" <filter-(E-Mail Removed)> escreveu na mensagem
news:(E-Mail Removed)...
> Hi Rob,
>
> For Each uses an enumerator behind the scenes so, as expected, on the
> tests that I did, they came out even (to the 3rd dec place). The
difference is
> almost certainly due to timng inaccuracies.
>
> On the other hand - using For I = 0 To al.Count - 1 was three times
> faster!
>
> Regards,
> Fergus
>
>
>

Hi Rafael,

For Each/IEnumerator does indeed advantages. Also the timing was done on a
loop which did very little (a single method call on the object and an
addition - so that it wouldn't all be optimised away). In practice the three
times faster of the For-I loop may well be trivial compared to the cost of the
work inside the loop.

Regards,
Fergus

Fergus,

Thanks for you post.

So if I have routines traversing lots of items in collections then the code
FOR NEXT (below) would be better than using FOR EACH? So I am guessing the
rule of thumb is to use FOR NEXT over FOR EACH for heavliy used routines.

Thanks,
Rob Panosh

Dim oItem AS Something
For i = 0 to al.count-1
oItem = al.Item(i)
' Do some processing
...
...
...
next

For Each oItem As Something In al
'Do some processing
...
...
...
Next



"Fergus Cooney" <filter-(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi Rob,
>
> For Each uses an enumerator behind the scenes so, as expected, on the
> tests that I did, they came out even (to the 3rd dec place). The
difference is
> almost certainly due to timng inaccuracies.
>
> On the other hand - using For I = 0 To al.Count - 1 was three times
> faster!
>
> Regards,
> Fergus
>
>
>

You forget one important factor also, FOR EACH takes alot of memory
(depending on your array size)
So, as stated, FOR NEXT is in most cases alot better.

Regards
Fredrik Melin

"Rob Panosh" <rob_!!!NO!!!SPAM!!!_(E-Mail Removed)> wrote in
message news:(E-Mail Removed)...
> Fergus,
>
> Thanks for you post.
>
> So if I have routines traversing lots of items in collections then the
code
> FOR NEXT (below) would be better than using FOR EACH? So I am guessing
the
> rule of thumb is to use FOR NEXT over FOR EACH for heavliy used routines.
>
> Thanks,
> Rob Panosh
>
> Dim oItem AS Something
> For i = 0 to al.count-1
> oItem = al.Item(i)
> ' Do some processing
> ...
> ...
> ...
> next
>
> For Each oItem As Something In al
> 'Do some processing
> ...
> ...
> ...
> Next
>
>
>
> "Fergus Cooney" <filter-(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > Hi Rob,
> >
> > For Each uses an enumerator behind the scenes so, as expected, on
the
> > tests that I did, they came out even (to the 3rd dec place). The
> difference is
> > almost certainly due to timng inaccuracies.
> >
> > On the other hand - using For I = 0 To al.Count - 1 was three times
> > faster!
> >
> > Regards,
> > Fergus
> >
> >
> >
>
>