Hi,
is it possible to have a recursive GetEnumerator for traversing a tree
structure ?
public IEnumerator<DTy peGetEnumerator ()
{
return GetEnumerator(r oot);
}
public IEnumerator<DTy peGetEnumerator (node p)
{
if(p.low!=null)
GetEnumerator(p .low);
yield return p.val;
if(p.high!=null )
GetEnumerator(p .high);
}
compiles ok, but foreach only does 1 iteration.
Colin =^.^=
16  4261 
"colin" <co*********@nt world.NOSPAM.co mwrote in message
news:VB******** ********@newsfe 6-win.ntli.net...
Hi,
is it possible to have a recursive GetEnumerator for traversing a tree
structure ?
public IEnumerator<DTy peGetEnumerator ()
{
return GetEnumerator(r oot);
}
public IEnumerator<DTy peGetEnumerator (node p)
{
if(p.low!=null)
GetEnumerator(p .low);
yield return p.val;
if(p.high!=null )
GetEnumerator(p .high);
}
compiles ok, but foreach only does 1 iteration.
Colin =^.^=
ah not to worry, i did the recursion by using recursive foreach instead of
the function call.
Colin =^.^=
colin wrote:
Hi,
is it possible to have a recursive GetEnumerator for traversing a tree
structure ?
public IEnumerator<DTy peGetEnumerator ()
{
return GetEnumerator(r oot);
}
public IEnumerator<DTy peGetEnumerator (node p)
{
if(p.low!=null)
GetEnumerator(p .low);
The GetEnumerator method returns an enumerator. If you just throw away
the return value, there is hardly any reason to make the call, is there.
yield return p.val;
Why is the code continuing after return? Did you ignore the compiler
warning about unreachable code?
if(p.high!=null )
GetEnumerator(p .high);
Once again, mind the return value.
}
compiles ok, but foreach only does 1 iteration.
You mean that it compiles, but with warnings...
--
Göran Andersson
_____ http://www.guffa.com
"Göran Andersson" <gu***@guffa.co mwrote in message
news:er******** ******@TK2MSFTN GP05.phx.gbl...
colin wrote:
>Hi,
is it possible to have a recursive GetEnumerator for traversing a tree
structure ?
public IEnumerator<DTy peGetEnumerator ()
{
return GetEnumerator(r oot);
}
public IEnumerator<DTy peGetEnumerator (node p)
{
if(p.low!=null )
GetEnumerator( p.low);
The GetEnumerator method returns an enumerator. If you just throw away the
return value, there is hardly any reason to make the call, is there.
I dont think in this case it actually returns anything, at least not thats
used.
if I try and return an IEnumerator it complains.
>
>yield return p.val;
Why is the code continuing after return? Did you ignore the compiler
warning about unreachable code?
thats the nature of yield I beleive, however this is the first time ive used
it,
so im a bit unsure, but it seems it just yields control, doesnt actually
realy return.
ie when it comes accros a 'yield return expresion' it executs
the code inside the foreach loop with the value in expresion
when that code has executed, it continues after the 'yield return expresion'
statement
>
>if(p.high!=nul l)
GetEnumerator( p.high);
Once again, mind the return value.
its recursive so the value isnt used from the return as such, but from the
yield statement.
>compiles ok, but foreach only does 1 iteration.
You mean that it compiles, but with warnings...
dont think there were any warnings at all,
however ive since used foreach instead of calling another GetEnumerator
and it works ok...
so getenumerator does foreach wich calls getenumerator and does foreach
recursivly for all the trees nodes.
Colin =^.^=
Hi,
I had to implement in in C# 3.0. There is nothing very C# 3.0 special there,
so you can easily translate it back to C# 2.0.
public static IEnumerable<TTr averseTree<T>(t his IEnumerable<Tse lf,
Func<T, IEnumerable<T>g etChildren)
{
var parents = new Stack<IEnumerat or<T>>();
var enumerator = self.GetEnumera tor();
parents.Push(en umerator);
do
{
enumerator = parents.Pop();
while (enumerator.Mov eNext())
{
var current = enumerator.Curr ent;
yield return current;
parents.Push(en umerator);
enumerator = getChildren(cur rent).GetEnumer ator();
}
}
while (parents.Count 0);
}
If you know your types you may replace getChildren with your actual method
that returns enumerator of node children.
-yuriy http://couldbedone.blogspot.com
"Göran Andersson" <gu***@guffa.co mwrote in message
news:er******** ******@TK2MSFTN GP05.phx.gbl...
>colin wrote:
>>Hi,
is it possible to have a recursive GetEnumerator for traversing a
tree
structure ?
public IEnumerator<DTy peGetEnumerator ()
{
return GetEnumerator(r oot);
}
public IEnumerator<DTy peGetEnumerator (node p)
{
if(p.low!=nul l)
GetEnumerator (p.low);
The GetEnumerator method returns an enumerator. If you just throw
away the return value, there is hardly any reason to make the call,
is there.
I dont think in this case it actually returns anything, at least not
thats
used.
if I try and return an IEnumerator it complains.
>>yield return p.val;
Why is the code continuing after return? Did you ignore the compiler
warning about unreachable code?
thats the nature of yield I beleive, however this is the first time
ive used
it,
so im a bit unsure, but it seems it just yields control, doesnt
actually
realy return.
ie when it comes accros a 'yield return expresion' it executs
the code inside the foreach loop with the value in expresion
when that code has executed, it continues after the 'yield return
expresion'
statement
>>if(p.high!=nu ll)
GetEnumerator (p.high);
Once again, mind the return value.
its recursive so the value isnt used from the return as such, but from
the yield statement.
>>compiles ok, but foreach only does 1 iteration.
You mean that it compiles, but with warnings...
dont think there were any warnings at all,
however ive since used foreach instead of calling another
GetEnumerator
and it works ok...
so getenumerator does foreach wich calls getenumerator and does
foreach recursivly for all the trees nodes.
Colin =^.^=
"Yuriy Solodkyy" <y.************ @gmail.comwrote in message
news:8a******** *************** ****@msnews.mic rosoft.com...
Hi,
I had to implement in in C# 3.0. There is nothing very C# 3.0 special
there, so you can easily translate it back to C# 2.0.
public static IEnumerable<TTr averseTree<T>(t his IEnumerable<T>
self, Func<T, IEnumerable<T>g etChildren)
{
var parents = new Stack<IEnumerat or<T>>();
var enumerator = self.GetEnumera tor();
parents.Push(en umerator);
do
{
enumerator = parents.Pop();
while (enumerator.Mov eNext())
{
var current = enumerator.Curr ent; yield return current;
parents.Push(en umerator);
enumerator = getChildren(cur rent).GetEnumer ator();
}
}
while (parents.Count 0);
}
If you know your types you may replace getChildren with your actual method
that returns enumerator of node children.
I was hoping to do it recursivly rather than remember all the parent nodes
for each entry.
I think its a bit simpler and could be faster,
however ive no idea how this looks in actual implementaion.
I made the nodes themselves enumerable thus :-
public IEnumerator<DTy peGetEnumerator ()
{
if (low != null)
foreach (DType x in low)
yield return x;
yield return val;
if (high != null)
foreach (DType x in high)
yield return x;
}
sp the main class GetEnumerator just calls foreach on the root node.
I confess to not fully understanding what im doing however,
I picked up a bit from examples, although the recursive took a while to
figure out.
ive ignored the MoveNext and Current as it doesnt fit with doing it
recursivly.
im not sure if Il need it anyway, but it seems to work ok.
I got realy confused with the difference between interfaces and
generic/non-generic bases etc.
Colin =^.^=
colin wrote:
I dont think in this case it actually returns anything, at least not thats
used.
if I try and return an IEnumerator it complains.
Yes, it does return an enumerator. (Or, at least, it works as if it
returns an enumerator. I don't know exactly how it's implemented.)
>>yield return p.val;
Why is the code continuing after return? Did you ignore the compiler
warning about unreachable code?
thats the nature of yield I beleive,
Yes, you are right. The code continues at that point for the next step
in the enumeration.
--
Göran Andersson
_____ http://www.guffa.com
"Göran Andersson" <gu***@guffa.co mwrote in message
news:%2******** ********@TK2MSF TNGP03.phx.gbl. ..
colin wrote:
>I dont think in this case it actually returns anything, at least not
thats used.
if I try and return an IEnumerator it complains.
Yes, it does return an enumerator. (Or, at least, it works as if it
returns an enumerator. I don't know exactly how it's implemented.)
it seems to actually return the data not the enumerator,
well it complains if you do,
I gues IEnumerator is just a sort of keyword to say its not a normal
function.
im not sure what happens if you actually return data without yield,
wether it gets called for each element, I gues thats what the Next and
Current would be for.
Colin =^.^=
On Jun 25, 12:04 pm, "colin" <colin.ro...@nt world.NOSPAM.co mwrote:
Yes, it does return an enumerator. (Or, at least, it works as if it
returns an enumerator. I don't know exactly how it's implemented.)
it seems to actually return the data not the enumerator,
well it complains if you do,
I gues IEnumerator is just a sort of keyword to say its not a normal
function.
No, not at all. GetEnumerator returns an enumerator. That enumerator
is then used to fetch an IEnumerable, which has the MoveNext and
Current members.
foreach does all this for you under the hood.
im not sure what happens if you actually return data without yield,
wether it gets called for each element, I gues thats what the Next and
Current would be for.
yield return is just smart syntactic sugar which builds an IEnumerator/
IEnumerable.
You can use ildasm or reflector to see what types are in your compiled
code.
It's worth understanding what foreach does before you embark on C# 2's
iterator-building features.
Jon
"Jon Skeet [C# MVP]" <sk***@pobox.co mwrote in message
news:11******** **************@ c77g2000hse.goo glegroups.com.. .
On Jun 25, 12:04 pm, "colin" <colin.ro...@nt world.NOSPAM.co mwrote:
Yes, it does return an enumerator. (Or, at least, it works as if it
returns an enumerator. I don't know exactly how it's implemented.)
it seems to actually return the data not the enumerator,
well it complains if you do,
I gues IEnumerator is just a sort of keyword to say its not a normal
function.
No, not at all. GetEnumerator returns an enumerator. That enumerator
is then used to fetch an IEnumerable, which has the MoveNext and
Current members.
foreach does all this for you under the hood.
>im not sure what happens if you actually return data without yield,
wether it gets called for each element, I gues thats what the Next and
Current would be for.
yield return is just smart syntactic sugar which builds an IEnumerator/
IEnumerable.
You can use ildasm or reflector to see what types are in your compiled
code.
It's worth understanding what foreach does before you embark on C# 2's
iterator-building features.
thanks,
well im only using foreach on this tree to check the rest of it is working,
so I dont intend to make it too elaborate,
like i said before, the current and move next arnt very usefull in a tree,
unless the parent nodes are stored as well wich is messy.
with recursive calls they are stored but on the call stack.
I dont think I will be needing to use the iterator outside a foreach loop,
so I think im safe.
I think its realy quite neat you can use foreach to iterate a list like
this,
before in c++ I had to pass a function and all other data it needed to an
iterator,
and wich made it a bit more limited.
the complexity of the many different types that have to do with collections
however has overflowed my brain for now,
im not even sure if I realy need to inherit any of them,
the complexities of extracting nodes in a tree
and balancing it is enough to cope with for 1 day.
Colin =^.^= This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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