The HashSet(Of T) class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no ...
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C#Setcollection?
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13years,5monthsago
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DoesanyoneknowifthereisagoodequivalenttoJava'sSetcollectioninC#?IknowthatyoucansomewhatmimicasetusingaDictionaryoraHashTablebypopulatingbutignoringthevalues,butthat'snotaveryelegantway.
c#.netcollectionsset
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editedAug22,2013at10:13
OmarKooheji
askedOct8,2008at16:33
OmarKoohejiOmarKooheji
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Sortedby:
Resettodefault
Highestscore(default)
Datemodified(newestfirst)
Datecreated(oldestfirst)
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Ifyou'reusing.NET3.5,youcanuseHashSet.It'struethat.NETdoesn'tcaterforsetsaswellasJavadoesthough.
TheWintellectPowerCollectionsmayhelptoo.
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editedMar1,2012at20:10
Sam
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answeredOct8,2008at16:36
JonSkeetJonSkeet
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IsuspectthatSetisakeywordinsomelanguages,whichcouldcauseissues.
– JonSkeet
Jun24,2009at8:10
5
@Manish:Noit'snot.Seesection2.4.3oftheC#3spec.Itonlyhasspecialmeaningforproperties.
– JonSkeet
Apr17,2010at6:40
31
ThereasonforcallingitHashSet,insteadofjustSet,isthesameasinJava-"Set"describesaninterface,whereas"HashSet"describesanimplementation-specifically,thisisaSetbackedbyaHashMap.Inthisway,weknow(orshouldstronglyexpect)thatinsertandaccessshouldtakeO(1)accesstime,vsa"LinkedListSet"whichwouldleadustoexpectinsertandaccesstotakeO(n)time.
– DavidSouther
Jul16,2010at16:16
6
whatdoyoumean".NETdoesn'tcaterforsetsaswellasJavadoesthough."?IsthisSetsomehowimperfectcomparedtoJava's?
– LouisRhys
Feb28,2011at3:13
37
@Louis:WhichSetareyoutalkingabout?JavahaslotsofdifferentimplementationsofSetforvarioussituations..NEThadonein.NET3.5(HashSet)andtwoin.NET4(HashSetandSortedSet).Thefactthatwehadtowaituntil.NET3.5tostartwithisprettysurprising.
– JonSkeet
Feb28,2011at8:20
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TryHashSet:
TheHashSet(Of T)classprovideshigh-performancesetoperations.Asetisacollectionthatcontainsnoduplicateelements,andwhoseelementsareinnoparticularorder...
ThecapacityofaHashSet(Of T)objectisthenumberofelementsthattheobjectcanhold.AHashSet(Of T)object'scapacityautomaticallyincreasesaselementsareaddedtotheobject.
TheHashSet(Of T)classisbasedonthemodelofmathematicalsetsandprovideshigh-performancesetoperationssimilartoaccessingthekeysoftheDictionary(Of TKey, TValue)orHashtablecollections.Insimpleterms,theHashSet(Of T)classcanbethoughtofasaDictionary(Of TKey, TValue)collectionwithoutvalues.
AHashSet(Of T)collectionisnotsortedandcannotcontainduplicateelements...
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editedOct1,2016at20:26
gnat
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answeredOct8,2008at16:35
LeahnNovashLeahnNovash
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Unfortunately,HashSetsweren'taddeduntiljustrecently.Ifyou'reworkinginanolderversionoftheframework,you'regoingtohavetostickwithyourmungedDictionary<>orHashtable.
– GregD
Oct8,2008at16:36
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Ifyou'reusing.NET4.0orlater:
InthecasewhereyouneedsortingthenuseSortedSet.Otherwiseifyoudon't,thenuseHashSetsinceit'sO(1)forsearchandmanipulateoperations.WhereasSortedSetisO(logn)forsearchandmanipulateoperations.
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editedAug31,2013at22:17
answeredAug31,2013at18:01
DerekWDerekW
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IuseIesi.Collectionshttp://www.codeproject.com/KB/recipes/sets.aspx
It'susedinlotofOSSprojects,IfirstcameacrossitinNHibernate
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answeredOct8,2008at16:36
ChrisCanalChrisCanal
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IuseawrapperaroundaDictionary,storingnullsinthevalues.ThisgivesO(1)add,lookupandremoveonthekeys,andtoallintentsandpurposesactslikeaset.
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answeredNov26,2009at1:08
thecoopthecoop
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Youmustmeanit'sroughlyequivalenttostd::unordered_set.std::setisordered.Forexample,youcanquicklyfindthestartandendpointofarangeanditeratefromthestarttotheend,visitingitemsinkey-order.SortedDictionaryisroughlyequivalenttostd::set.
– doug65536
Feb4,2013at7:43
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HavealookatPowerCollectionsoveratCodePlex.ApartfromSetandOrderedSetithasafewotherusefullcollectiontypessuchasDeque,MultiDictionary,Bag,OrderedBag,OrderedDictionaryandOrderedMultiDictionary.
Formorecollections,thereisalsotheC5GenericCollectionLibrary.
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editedOct8,2008at16:50
answeredOct8,2008at16:38
dpandpan
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Iknowthisisanoldthread,butIwasrunningintothesameproblemandfoundHashSettobeveryunreliablebecausegiventhesameseed,GetHashCode()returneddifferentcodes.So,Ithought,whynotjustuseaListandhidetheaddmethodlikethis
publicclassUniqueList:List
{
publicnewvoidAdd(Tobj)
{
if(!Contains(obj))
{
base.Add(obj);
}
}
}
BecauseListusestheEqualsmethodsolelytodetermineequality,youcandefinetheEqualsmethodonyourTtypetomakesureyougetthedesiredresults.
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editedFeb4,2012at23:01
answeredFeb4,2012at22:50
BobHeckBobHeck
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Thereasonyouwouldn'twanttousethisisbecauseList.ContainsisofO(n)complexitywhichmeansthatyourAddmethodnowbecomesO(n)complexityaswell.Assumingtheinnercollectiondoesn'tneedtoberesized,AddforbothListandHashMapshouldbeofO(1)complexity.TLDR:Thiswillwork,butit'shackyandlessefficient.
– RichardMarskell-Drackir
Feb24,2012at20:28
6
Sure,ifyourobjectsdon'treturnanappropriatevalueforGetHashCode,youshouldnotputthemintoahash-basedcontainer.ItwouldbebettertofixGetHashCodethantousealessefficientcontainer.
– bmm6o
Mar5,2012at17:40
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