Intersect Two Lists in C

Question

I have two lists     List lt int gt  data1   new List lt int gt   1 2 3 4 5     List lt string gt  data2   new List lt string gt   6   3      I want do to something like   var newData   data1 intersect data2  lambda expression     The lambda expression should return true if data1 index  ToString      data2 index

User · Answer

If you have objects  not structs  or strings   then you ll have to intersect their keys first  and then select objects by those keys   var ids   list1 Select x   gt  x Id  Intersect list2 Select x   gt  x Id    var result   list1 Where x   gt  ids Contains x Id

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From performance point of view if two lists contain number of elements that differ significantly  you can try such approach  using conditional operator       1 First you need to declare a converter   Converter lt string  int gt  del   delegate string s    return Int32 Parse s        2 Then you use a conditional operator   var r   data1 Count  gt  data2 Count    data2 ConvertAll lt int gt  del  Intersect data1     data1 Select v   gt  v ToString    Intersect data2  ToList lt string gt    ConvertAll lt int gt  del     You convert elements of shorter list to match the type of longer list  Imagine an execution speed if your first set contains 1000 elements and second only 10  or opposite as it doesn t matter   -   As you want to have a result as List  in a last line you convert the result  only result  back to int

User · Answer

You need to first transform data1  in your case by calling ToString   on each element  Use this if you want to return strings  List lt int gt  data1   new List lt int gt   1 2 3 4 5   List lt string gt  data2   new List lt string gt   quot 6 quot   quot 3 quot     var newData   data1 Select i   gt  i ToString    Intersect data2     Use this if you want to return integers  List lt int gt  data1   new List lt int gt   1 2 3 4 5   List lt string gt  data2   new List lt string gt   quot 6 quot   quot 3 quot     var newData   data1 Intersect data2 Select s   gt  int Parse s     Note that this will throw an exception if not all strings are numbers  So you could do the following first to check  int temp  if data2 All s   gt  int TryParse s  out temp             All data2 strings are int s

User · Answer

public static List lt T gt  ListCompare lt T gt  List lt T gt  List1   List lt T gt  List2   string key         return List1 Select t   gt  t GetType   GetProperty key  GetValue t                    Intersect List2 Select t   gt  t GetType   GetProperty key  GetValue t    ToList

[c#] Intersect Two Lists in C#

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