How to compare two List String to each other

Question

Let s say there are   List lt string gt  a1   new List lt string gt      List lt string gt  a2   new List lt string gt       Is there way to do like this   if  a1    a2

User · Answer

I discovered that SequenceEqual is not the most efficient way to compare two lists of strings  initially from http   www dotnetperls com sequenceequal    I wanted to test this myself so I created two methods            lt summary gt          Compares two string lists using LINQ s SequenceEqual           lt  summary gt      public bool CompareLists1 List lt string gt  list1  List lt string gt  list2                return list1 SequenceEqual list2                   lt summary gt          Compares two string lists using a loop           lt  summary gt      public bool CompareLists2 List lt string gt  list1  List lt string gt  list2                if  list1 Count    list2 Count              return false           for  int i   0  i  lt  list1 Count  i                          if  list1 i     list2 i                   return false                     return true          The second method is a bit of code I encountered and wondered if it could be refactored to be  easier to read    And also wondered if LINQ optimization would be faster    As it turns out  with two lists containing 32k strings  over 100 executions    Method 1 took an average of 6761 8 ticks Method 2 took an average of 3268 4 ticks   I usually prefer LINQ for brevity  performance  and code readability  but in this case I think a loop-based method is preferred   Edit   I recompiled using optimized code  and ran the test for 1000 iterations  The results still favor the loop  even more so     Method 1 took an average of 4227 2 ticks Method 2 took an average of 1831 9 ticks   Tested using Visual Studio 2010  C   NET 4 Client Profile on a Core i7-920

User · Answer

If you want to check that the elements inside the list are equal and in the same order  you can use SequenceEqual   if  a1 SequenceEqual a2     See it working online  ideone

User · Answer

You can check in all the below ways for a List   List lt string gt  FilteredList   new List lt string gt       Comparing the two lists and gettings common elements  FilteredList   a1 Intersect a2  StringComparer OrdinalIgnoreCase

User · Answer

You could also use Except produces the set difference of two sequences  to check whether there s a difference or not  IEnumerable lt string gt  inFirstOnly   a1 Except a2   IEnumerable lt string gt  inSecondOnly   a2 Except a1   bool allInBoth    inFirstOnly Any    amp  amp   inSecondOnly Any     So this is an efficient way if the order and if the number of duplicates does not matter as opposed to the accepted answer s SequenceEqual   Demo  Ideone If you want to compare in a case insentive way  just add StringComparer OrdinalIgnoreCase  a1 Except a2  StringComparer OrdinalIgnoreCase

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private static bool CompareDictionaries IDictionary lt string  IEnumerable lt string gt  gt  dict1  IDictionary lt string  IEnumerable lt string gt  gt  dict2                if  dict1 Count    dict2 Count                        return false                     var keyDiff   dict1 Keys Except dict2 Keys           if  keyDiff Any                          return false                     return  from key in dict1 Keys                  let value1   dict1 key                   let value2   dict2 key                   select value1 Except value2   All diffInValues   gt   diffInValues Any

[c#] How to compare two List<String> to each other?

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