determine common members in list of lists

[John A Grandy]

InstrumentPrope rtyEntity
string Name

InstrumentEntit y
string Name
List<Instrument PropertyEntityI nstrumentProper ties
For a List<Instrument Entity, I want to determine the
List<Instrument PropertyEntityh eld in common by all members.
What is the most performant algorithm ?

[Pavel Minaev]

On Jul 18, 3:46*am, "John A Grandy" <johnagrandy-at-gmail-dot-com>
wrote:

InstrumentPrope rtyEntity
* * string Name

InstrumentEntit y
* * string Name
* * List<Instrument PropertyEntityI nstrumentProper ties

For a List<Instrument Entity, I want to determine the
List<Instrument PropertyEntityh eld in common by all members.

What is the most performant algorithm ?

If you need it to be fast, you shouldn't use List<T>. If
InstrumentPrope rties would have been of type HashSet<T>, then you
could use its IntersectWith method in a foreach loop to efficiently
find the intersection of InstrumentPrope rties for all your elements -
and that would be what you want. For plain List<T>, you can use
Enumerable.Inte rsect, but it's not any more efficient than a plain
nested foreach.

[John A Grandy]

How about transferring the contents of the first List to a HashSet and then
successively call HashSet.Interse ctWith( List ) for each remaining List ?

"Pavel Minaev" <in****@gmail.c omwrote in message
news:69******** *************** ***********@j1g 2000prb.googleg roups.com...
On Jul 18, 3:46 am, "John A Grandy" <johnagrandy-at-gmail-dot-com>
wrote:

InstrumentPrope rtyEntity
string Name

InstrumentEntit y
string Name
List<Instrument PropertyEntityI nstrumentProper ties

For a List<Instrument Entity, I want to determine the
List<Instrument PropertyEntityh eld in common by all members.

What is the most performant algorithm ?

If you need it to be fast, you shouldn't use List<T>. If
InstrumentPrope rties would have been of type HashSet<T>, then you
could use its IntersectWith method in a foreach loop to efficiently
find the intersection of InstrumentPrope rties for all your elements -
and that would be what you want. For plain List<T>, you can use
Enumerable.Inte rsect, but it's not any more efficient than a plain
nested foreach.

[John A Grandy]

Just noticed that HashSet was introduced in 3.5. I am on 2.0.

"John A Grandy" <johnagrandy-at-gmail-dot-comwrote in message
news:Ol******** ******@TK2MSFTN GP02.phx.gbl...

How about transferring the contents of the first List to a HashSet and
then successively call HashSet.Interse ctWith( List ) for each remaining
List ?

"Pavel Minaev" <in****@gmail.c omwrote in message
news:69******** *************** ***********@j1g 2000prb.googleg roups.com...
On Jul 18, 3:46 am, "John A Grandy" <johnagrandy-at-gmail-dot-com>
wrote:

>InstrumentProp ertyEntity
string Name

InstrumentEnti ty
string Name
List<Instrumen tPropertyEntity InstrumentPrope rties

For a List<Instrument Entity, I want to determine the
List<Instrumen tPropertyEntity held in common by all members.

What is the most performant algorithm ?

If you need it to be fast, you shouldn't use List<T>. If
InstrumentPrope rties would have been of type HashSet<T>, then you
could use its IntersectWith method in a foreach loop to efficiently
find the intersection of InstrumentPrope rties for all your elements -
and that would be what you want. For plain List<T>, you can use
Enumerable.Inte rsect, but it's not any more efficient than a plain
nested foreach.

[Pavel Minaev]

On Jul 18, 9:04*pm, "John A Grandy" <johnagrandy-at-gmail-dot-com>
wrote:

How about transferring the contents of the first List to a HashSet and then
successively call HashSet.Interse ctWith( List ) for each remaining List ?

InteesectWith requires the argument to be a HashSet as well, so you'll
need to convert both.

[John A Grandy]

How is IntersectWith determining equality ? Is it instance equality ? Or
does it compare the values of all members of each instance ?

My instance equality is based on the Name property only.

InstrumentPrope rty1.Name == InstrumentPrope rty2.Name
"Pavel Minaev" <in****@gmail.c omwrote in message
news:8e******** *************** ***********@z72 g2000hsb.google groups.com...
On Jul 18, 9:04 pm, "John A Grandy" <johnagrandy-at-gmail-dot-com>
wrote:

How about transferring the contents of the first List to a HashSet and
then
successively call HashSet.Interse ctWith( List ) for each remaining List ?

InteesectWith requires the argument to be a HashSet as well, so you'll
need to convert both.

[Pavel Minaev]

On Jul 18, 9:14*pm, "John A Grandy" <johnagrandy-at-gmail-dot-com>
wrote:

Just noticed that HashSet was introduced in 3.5. I am on 2.0.

You can always use Dictionary with dummy values - performance-wise,
it's the same as HashSet - but you'd still have to code Intersect
youself. Perhaps this would do the trick:

IEnumerable<TIn tersect<T>(IEnu merable<Txs, IEnumerable<Tys )
{
Dictionary<T, boolzs = new Dictionary<T, bool>();
foreach (T x in xs)
{
zs.Add(x, false);
}
foreach (T y in ys)
{
bool dummy;
if (zs.TryGetValue (y, out dummy))
{
zs[y] = true;
}
}
foreach (KeyValuePair<T , boolz in zs)
{
if (z.Value)
{
yield return z.Key;
}
}
}