Compare two List T objects for equality ignoring order

Question

Yet another list-comparing question   List lt MyType gt  list1  List lt MyType gt  list2    I need to check that they both have the same elements  regardless of their position within the list  Each MyType object may appear multiple times on a list  Is there a built-in function that checks this  What if I guarantee that each element appears only once in a list   EDIT  Guys thanks for the answers but I forgot to add something  the number of occurrences of each element should be the same on both lists

User · Answer

If you don t care about the number of occurrences  I would approach it like this   Using hash sets will give you better performance than simple iteration   var set1   new HashSet lt MyType gt  list1   var set2   new HashSet lt MyType gt  list2   return set1 SetEquals set2     This will require that you have overridden  GetHashCode   and implemented IEquatable lt MyType gt  on MyType

User · Answer

If you want them to be really equal  i e  the same items and the same number of each item   I think that the simplest solution is to sort before comparing   Enumerable SequenceEqual list1 OrderBy t   gt  t   list2 OrderBy t   gt  t     Edit   Here is a solution that performs a bit better  about ten times faster   and only requires IEquatable  not IComparable   public static bool ScrambledEquals lt T gt  IEnumerable lt T gt  list1  IEnumerable lt T gt  list2      var cnt   new Dictionary lt T  int gt       foreach  T s in list1        if  cnt ContainsKey s           cnt s           else         cnt Add s  1               foreach  T s in list2        if  cnt ContainsKey s           cnt s --        else         return false              return cnt Values All c   gt  c    0       Edit 2   To handle any data type as key  for example nullable types as Frank Tzanabetis pointed out   you can make a version that takes a comparer for the dictionary   public static bool ScrambledEquals lt T gt  IEnumerable lt T gt  list1  IEnumerable lt T gt  list2  IEqualityComparer lt T gt  comparer      var cnt   new Dictionary lt T  int gt  comparer

User · Answer

In addition to Guffa s answer  you could use this variant to have a more shorthanded notation      public static bool ScrambledEquals lt T gt  this IEnumerable lt T gt  list1  IEnumerable lt T gt  list2      var deletedItems   list1 Except list2  Any      var newItems   list2 Except list1  Any      return  newItems  amp  amp   deletedItems

User · Answer

try this     using following code you could compare one or many fields to generate a result list as per your need  result list will contain only modified item s       veriables been used List lt T gt  diffList   new List lt T gt     List lt T gt  gotResultList   new List lt T gt           compare First field within my MyList gotResultList   MyList1 Where a   gt   MyList2 Any a1   gt  a1 MyListTField1    a MyListTField1   ToList   Except gotResultList Where a   gt   MyList2 Any a1   gt  a1 MyListTField1    a MyListTField1    ToList       Generate result list diffList AddRange gotResultList       compare Second field within my MyList gotResultList   MyList1 Where a   gt   MyList2 Any a1   gt  a1 MyListTField2    a MyListTField2   ToList   Except gotResultList Where a   gt   MyList2 Any a1   gt  a1 MyListTField2    a MyListTField2    ToList       Generate result list diffList AddRange gotResultList     MessageBox Show diffList Count ToString

User · Answer

Thinking this should do what you want   list1 All item   gt  list2 Contains item    amp  amp  list2 All item   gt  list1 Contains item      if you want it to be distinct  you could change it to   list1 All item   gt  list2 Contains item    amp  amp  list1 Distinct   Count      list1 Count  amp  amp  list1 Count    list2 Count

User · Answer

This worked for me  If you are comparing two lists of objects depend upon single entity like ID  and you want a third list which matches that condition  then you can do the following   var list3   List1 Where n   gt   List2 select n1   gt  n1 Id  Contains n Id      Refer  MSDN - C  Compare Two lists of objects

User · Answer

This is a slightly difficult problem  which I think reduces to   Test if two lists are permutations of each other    I believe the solutions provided by others only indicate whether the 2 lists contain the same unique elements  This is a necessary but insufficient test  for example  1  1  2  3  is not a permutation of  3  3  1  2  although their counts are equal and they contain the same distinct elements   I believe this should work though  although it s not the most efficient   static bool ArePermutations lt T gt  IList lt T gt  list1  IList lt T gt  list2       if list1 Count    list2 Count           return false      var l1   list1 ToLookup t   gt  t      var l2   list2 ToLookup t   gt  t       return l1 Count    l2 Count          amp  amp  l1 All group   gt  l2 Contains group Key   amp  amp  l2 group Key  Count      group Count

User · Answer

I use this method    public delegate bool CompareValue lt in T1  in T2 gt  T1 val1  T2 val2    public static bool CompareTwoArrays lt T1  T2 gt  this IEnumerable lt T1 gt  array1  IEnumerable lt T2 gt  array2  CompareValue lt T1  T2 gt  compareValue        return array1 Select item1   gt  array2 Any item2   gt  compareValue item1  item2    All search   gt  search               amp  amp  array2 Select item2   gt  array1 Any item1   gt  compareValue item1  item2    All search   gt  search

User · Answer

As written  this question is ambigous  The statement          they both have the same elements  regardless of their position within the list     Each MyType object may appear multiple times on a list     does not indicate whether you want to ensure that the two lists have the same set of objects or the same distinct set   If you want to ensure to collections have exactly the same set of members regardless of order  you can use      lists should have same count of items  and set difference must be empty var areEquivalent    list1 Count    list2 Count   amp  amp   list1 Except list2  Any      If you want to ensure two collections have the same distinct set of members  where duplicates in either are ignored   you can use      check that   A-B  Union  B-A   is empty var areEquivalent    list1 Except list2  Union  list2 Except list1    Any      Using the set operations  Intersect  Union  Except  is more efficient than using methods like Contains  In my opinion  it also better expresses the expectations of your query   EDIT  Now that you ve clarified your question  I can say that you want to use the first form - since duplicates matter  Here s a simple example to demonstrate that you get the result you want   var a   new    1  2  3  4  4  3  1  1  2   var b   new     4  3  2  3  1  1  1  4  2        result below should be true  since the two sets are equivalent    var areEquivalent    a Count      b Count     amp  amp   a Except b  Any

[c#] Compare two List<T> objects for equality, ignoring order

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