ForEach & Remove Problem

**Michael D. Ober** · Jul 6 '06, 03:15 AM

Re: ForEach & Remove Problem

In VB 2005, use

for i as Integer in collection.coun t -1 to 0 step -1
if collection(i) = condition then collection.remo veat(i)
next i

Iterators don't like removing objects.

Mike Ober.

"Robert W." <RobertW@discus sions.microsoft .comwrote in message
news:963230B3-3CEA-448C-85E8-874A6092EB0C@mi crosoft.com...

Here's some pseudo-code that describes what I'm trying to do:
>
foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}
>
The problem with this is that foreach gets messed up if anything is

deleted

from the collection. What's the best way to handle such a situation?
>
--
Robert W.
Vancouver, BC

https://www.mwtech.com

>
>

**Robert W.** · Jul 6 '06, 03:35 AM

Re: ForEach & Remove Problem

And in C# 2003 ?

--
Robert W.
Vancouver, BC

https://www.mwtech.com

"Michael D. Ober" wrote:

In VB 2005, use
>
for i as Integer in collection.coun t -1 to 0 step -1
if collection(i) = condition then collection.remo veat(i)
next i
>
Iterators don't like removing objects.
>
Mike Ober.
>
"Robert W." <RobertW@discus sions.microsoft .comwrote in message
news:963230B3-3CEA-448C-85E8-874A6092EB0C@mi crosoft.com...

Here's some pseudo-code that describes what I'm trying to do:

foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}

The problem with this is that foreach gets messed up if anything is

deleted

from the collection. What's the best way to handle such a situation?

--
Robert W.
Vancouver, BC

https://www.mwtech.com

>
>
>
>

**Mark Wilden** · Jul 6 '06, 03:45 AM

Re: ForEach & Remove Problem

"Robert W." <RobertW@discus sions.microsoft .comwrote in message
news:596E5BD3-D6E0-41DF-8CB5-260287010025@mi crosoft.com...

>for i as Integer in collection.coun t -1 to 0 step -1
> if collection(i) = condition then collection.remo veat(i)
>next i

And in C# 2003 ?

Oh, c'mon. At least make an -effort-.

///ark

**Nicholas Paldino [.NET/C# MVP]** · Jul 6 '06, 03:45 AM

Re: ForEach & Remove Problem

Robert,

It doesn't matter, this has been a limitation in C# from version 1.0
(for good reason).

--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"Robert W." <RobertW@discus sions.microsoft .comwrote in message
news:596E5BD3-D6E0-41DF-8CB5-260287010025@mi crosoft.com...

And in C# 2003 ?
>
--
Robert W.
Vancouver, BC

https://www.mwtech.com

>
>
>
"Michael D. Ober" wrote:
>

>In VB 2005, use
>>
>for i as Integer in collection.coun t -1 to 0 step -1
> if collection(i) = condition then collection.remo veat(i)
>next i
>>
>Iterators don't like removing objects.
>>
>Mike Ober.
>>
>"Robert W." <RobertW@discus sions.microsoft .comwrote in message
>news:963230B 3-3CEA-448C-85E8-874A6092EB0C@mi crosoft.com...

Here's some pseudo-code that describes what I'm trying to do:
>
foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}
>
The problem with this is that foreach gets messed up if anything is

>deleted

from the collection. What's the best way to handle such a situation?
>
--
Robert W.
Vancouver, BC

https://www.mwtech.com

>
>

>>
>>
>>
>>

**Robert W.** · Jul 6 '06, 04:15 AM

Re: ForEach & Remove Problem

I don't know if this is the optimum solution, but here's what I've come up:

int i = 0;
do
{
ObjectClass object = collection[i];
if (test == false)
i++;
else
collection.Remo ve(object);
} while (i < collection.Coun t);

--
Robert W.
Vancouver, BC

https://www.mwtech.com

"Nicholas Paldino [.NET/C# MVP]" wrote:

Robert,
>
It doesn't matter, this has been a limitation in C# from version 1.0
(for good reason).
>
>
--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m
>
"Robert W." <RobertW@discus sions.microsoft .comwrote in message
news:596E5BD3-D6E0-41DF-8CB5-260287010025@mi crosoft.com...

And in C# 2003 ?

--
Robert W.
Vancouver, BC

https://www.mwtech.com

"Michael D. Ober" wrote:

In VB 2005, use
>
for i as Integer in collection.coun t -1 to 0 step -1
if collection(i) = condition then collection.remo veat(i)
next i
>
Iterators don't like removing objects.
>
Mike Ober.
>
"Robert W." <RobertW@discus sions.microsoft .comwrote in message
news:963230B3-3CEA-448C-85E8-874A6092EB0C@mi crosoft.com...
Here's some pseudo-code that describes what I'm trying to do:

foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}

The problem with this is that foreach gets messed up if anything is
deleted
from the collection. What's the best way to handle such a situation?

--
Robert W.
Vancouver, BC

https://www.mwtech.com

>
>
>
>

>
>
>

**John B** · Jul 6 '06, 05:45 AM

Re: ForEach & Remove Problem

Robert W. wrote:

I don't know if this is the optimum solution, but here's what I've come up:
>
int i = 0;
do
{
ObjectClass object = collection[i];
if (test == false)
i++;
else
collection.Remo ve(object);
} while (i < collection.Coun t);
>
>
>
>

Try a reverse for loop;

for(int i = col.Count -1; i >= 0; i--)
{
if(..test..)
{
col.Remove(i);
}
}

**Christian SchÃ¶nig** · Jul 6 '06, 07:45 AM

Re: ForEach & Remove Problem

Hi Robert,

I solved it like this:

SortedList temp=new SortedList(clie ntsUse);
foreach (object key in temp.Keys)
{
if (key.Equals(lbC lients.Selected Item)) clientsUse.Remo ve(key);
}

So make a copy and remove the stuff from the original list You have copied from!

Problem solved?

Chris

"Robert W." <RobertW@discus sions.microsoft .comschrieb im Newsbeitrag news:963230B3-3CEA-448C-85E8-874A6092EB0C@mi crosoft.com...

Here's some pseudo-code that describes what I'm trying to do:

foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}

The problem with this is that foreach gets messed up if anything is deleted
from the collection. What's the best way to handle such a situation?

--
Robert W.
Vancouver, BC

https://www.mwtech.com

>

**david ullua** · Jul 6 '06, 08:15 AM

Re: ForEach & Remove Problem

You can use for statement both in VS 2005 or 2003:

for( int i=collection.Co unt;i>=0;i--)
{
//...
}

Robert W. wrote:

Here's some pseudo-code that describes what I'm trying to do:
>
foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}
>
The problem with this is that foreach gets messed up if anything is deleted
from the collection. What's the best way to handle such a situation?
>
--
Robert W.
Vancouver, BC
www.mwtech.com

**Larry Lard** · Jul 6 '06, 09:45 AM

Re: ForEach & Remove Problem

Robert W. wrote:

Here's some pseudo-code that describes what I'm trying to do:
>
foreach(object in collection)
{
if (certain-condition)
collection.Remo ve(object);
}
>
The problem with this is that foreach gets messed up if anything is deleted
from the collection. What's the best way to handle such a situation?

The solutions offered you that rely on iterating by an index might well
work, but make me think 'yuck' when I read them. I would prefer:

// terrible pseudocode follows
// keepthese will hold the objects we want to keep
collection keepthese = new collection
foreach object in originalcollect ion
// if not removing this object, then keep it
if (!removalcondit ion)
keepthese.add(o bject);

// now we have just those objects we want to keep
// so keep them
originalcollect ion = keepthese;

For anyone worried about the cost of this, remember there is no actual
copying of objects here, just copying of references, which is cheap.

--
Larry Lard
Replies to group please
When starting a new topic, please mention which version of VB/C# you
are using

**John Duval** · Jul 6 '06, 10:55 AM

Re: ForEach & Remove Problem

Hi Robert,
It might be simplest for you just to iterate backwards through the
collection, but Eric Gunnerson had a good article on an "IterIsolat e"
utility class that handles cases like this. You might want to check
out his MSDN article:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dncscol/html/csharp01212002.asp

John

**Ignacio Machin \( .NET/ C# MVP \)** · Jul 6 '06, 01:35 PM

Re: ForEach & Remove Problem

Hi,

I also prefer a reverse loop, it does not affect the index.

Another possible solution that can be used in a collection that cannot be
used with index is using a temporary list to hold the values being deleted:

ArrayList ar = new ArrayList();

foreach(object o in collection)
{
if (certain-condition)
ar.Add(o);
}

foreach(object o in ar)
coollection.Rem ove( o);

--
--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

>>

Try a reverse for loop;
>
for(int i = col.Count -1; i >= 0; i--)
{
if(..test..)
{
col.Remove(i);
}
}

ForEach & Remove Problem

ForEach & Remove Problem

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