Linq select object from list depending on objects attribute

Question

I have a list of objects   class Answer      bool correct     List lt Answer gt  Answers   new List lt Answer gt       Is there a way in linq for me to select an object depending on its attribute   So far I have  Answer answer   Answers Single a   gt  a    a Correct     But it does not work

User · Answer

Of course   Use FirstOrDefault   to select the first object which matches the condition   Answer answer   Answers FirstOrDefault a   gt  a Correct     Otherwise use Where   to select a subset of your list   var answers   Answers Where a   gt  a Correct

User · Answer

if a Correct is a bool flag for the correct answer then you need    Answer answer   Answers Single a   gt  a Correct

User · Answer

First  Single throws an exception if there is more than one element satisfying the criteria  Second  your criteria should only check if the Correct property is true  Right now  you are checking if a is equal to a Correct  which will not even compile    You should use First  which will throw if there are no such elements   or FirstOrDefault  which will return null for a reference type if there isn t such element       this will return the first correct answer     or throw an exception if there are no correct answers var correct   answers First a   gt  a Correct        this will return the first correct answer      or null if there are no correct answers var correct   answers FirstOrDefault a   gt  a Correct        this will return a list containing all answers which are correct     or an empty list if there are no correct answers var allCorrect   answers Where a   gt  a Correct  ToList

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I think you are looking for this   var correctAnswer   Answers First a   gt  a Correct     You can use single by typing    var correctAnswer   Answers Single a   gt  a Correct

User · Answer

Your expression is never going to evaluate   You are comparing a with a property of a   a is of type Answer   a Correct  I m guessing is a boolean   Long form -  Answer   answer SingleOrDefault a   gt  a Correct    true     Short form -  Answer   answer SingleOrDefault a   gt  a Correct

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Answers   Answers GroupBy a   gt  a id  Select x   gt  x First       This will select each unique object by email

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Few things to fix here    No parenthesis in class declaration Make the  correct  property as public And then do the selection   Your code will look something like this  List lt Answer gt  answers   new List lt Answer gt        test answers Add new Answer     correct   false     answers Add new Answer     correct   true     answers Add new Answer     correct   false        Answer answer   answers Single a   gt  a correct    true     and the class  class Answer      public bool correct

User · Answer

I assume you are getting an exception because of Single  Your list may have more than one answer marked as correct  that is why Single will throw an exception use First  or FirstOrDefault     Answer answer   Answers FirstOrDefault a   gt  a Correct     Also if you want to get list of all items marked as correct you may try   List lt Answer gt  correctedAnswers    Answers Where a   gt  a Correct  ToList      If your desired result is Single  then the mistake you are doing in your query is comparing an item with the bool value  Your comparison  a    a Correct   is wrong in the statement   Your single query should be   Answer answer   Answers Single a   gt  a Correct    true     Or shortly as   Answer answer   Answers Single a   gt  a Correct

[c#] Linq select object from list depending on objects attribute

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