How to perform Max on a property of all objects in a collection and return the object with maximum value

Question

I have a list of objects that have two int properties  The list is the output of another linq query  The object   public class DimensionPair         public int Height   get  set        public int Width   get  set        I want to find and return the object in the list which has the largest Height property value   I can manage to get the highest value of the Height value but not the object itself   Can I do this with Linq  How

User · Answer

I believe that sorting by the column you want to get the MAX of and then grabbing the first should work   However  if there are multiple objects with the same MAX value  only one will be grabbed   private void Test         test v1   new test        v1 Id   12       test v2   new test        v2 Id   12       test v3   new test        v3 Id   12       List lt test gt  arr   new List lt test gt         arr Add v1       arr Add v2       arr Add v3        test max   arr OrderByDescending t   gt  t Id  First       class test       public int Id   get  set

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Doing an ordering and then selecting the first item is wasting a lot of time ordering the items after the first one  You don t care about the order of those   Instead you can use the aggregate function to select the best item based on what you re looking for   var maxHeight   dimensions      Aggregate  agg  next    gt           next Height  gt  agg Height   next   agg    var maxHeightAndWidth   dimensions      Aggregate  agg  next    gt           next Height  gt   agg Height  amp  amp  next Width  gt   agg Width   next  agg

User · Answer

And why don t you try with this        var itemsMax   items Where x   gt  x Height    items Max y   gt  y Height      OR more optimise    var itemMaxHeight   items Max y   gt  y Height   var itemsMax   items Where x   gt  x Height    itemMaxHeight     mmm

User · Answer

The answers so far are great  But I see a need for a solution with the following constraints    Plain  concise LINQ  O n  complexity  Do not evaluate the property more than once per element    Here it is   public static T MaxBy lt T  R gt  this IEnumerable lt T gt  en  Func lt T  R gt  evaluate  where R   IComparable lt R gt        return en Select t   gt  new Tuple lt T  R gt  t  evaluate t             Aggregate  max  next    gt  next Item2 CompareTo max Item2   gt  0   next   max  Item1     public static T MinBy lt T  R gt  this IEnumerable lt T gt  en  Func lt T  R gt  evaluate  where R   IComparable lt R gt        return en Select t   gt  new Tuple lt T  R gt  t  evaluate t             Aggregate  max  next    gt  next Item2 CompareTo max Item2   lt  0   next   max  Item1      Usage   IEnumerable lt Tuple lt string  int gt  gt  list   new         new Tuple lt string  int gt   other   2       new Tuple lt string  int gt   max   4       new Tuple lt string  int gt   min   1       new Tuple lt string  int gt   other   3      Tuple lt string  int gt  min   list MinBy x   gt  x Item2       min   1 Tuple lt string  int gt  max   list MaxBy x   gt  x Item2       max   4

User · Answer

You can also upgrade Mehrdad Afshari s solution by rewriting the extention method to faster  and better looking  one   static class EnumerableExtensions       public static T MaxElement lt T  R gt  this IEnumerable lt T gt  container  Func lt T  R gt  valuingFoo  where R   IComparable               var enumerator   container GetEnumerator            if   enumerator MoveNext                throw new ArgumentException  Container is empty              var maxElem   enumerator Current          var maxVal   valuingFoo maxElem            while  enumerator MoveNext                          var currVal   valuingFoo enumerator Current                if  currVal CompareTo maxVal   gt  0                                maxVal   currVal                  maxElem   enumerator Current                                   return maxElem            And then just use it   var maxObject   list MaxElement item   gt  item Height     That name will be clear to people using C    because there is std  max element in there

User · Answer

We have an extension method to do exactly this in MoreLINQ  You can look at the implementation there  but basically it s a case of iterating through the data  remembering the maximum element we ve seen so far and the maximum value it produced under the projection   In your case you d do something like   var item   items MaxBy x   gt  x Height     This is better  IMO  than any of the solutions presented here other than Mehrdad s second solution  which is basically the same as MaxBy     It s O n  unlike the previous accepted answer which finds the maximum value on every iteration  making it O n 2   The ordering solution is O n log n  Taking the Max value and then finding the first element with that value is O n   but iterates over the sequence twice  Where possible  you should use LINQ in a single-pass fashion  It s a lot simpler to read and understand than the aggregate version  and only evaluates the projection once per element

User · Answer

In NHibernate   with NHibernate Linq  you could do it as follows   return session Query lt T gt                   Single a   gt  a Filter    filter  amp  amp                             a Id    session Query lt T gt                                               Where a2   gt  a2 Filter    filter                                             Max a2   gt  a2 Id      Which will generate SQL like follows   select   from TableName foo where foo Filter    Filter On String  and foo Id    select cast max bar RowVersion  as INT                from TableName bar               where bar Name    Filter On String     Which seems pretty efficient to me

User · Answer

Based on Cameron s initial answer  here is what I ve just added at my enhanced version of SilverFlow library s FloatingWindowHost  copying from FloatingWindowHost cs at http   clipflair codeplex com source code       public int MaxZIndex             get           return FloatingWindows Aggregate -1   maxZIndex  window    gt              int w   Canvas GetZIndex window             return  w  gt  maxZIndex    w   maxZIndex                                 private void SetTopmost UIElement element                if  element    null              throw new ArgumentNullException  element             Canvas SetZIndex element  MaxZIndex   1           Worth noting regarding the code above that Canvas ZIndex is an attached property available for UIElements in various containers  not just used when being hosted in a Canvas  see Controlling rendering order  ZOrder  in Silverlight without using the Canvas control   Guess one could even make a SetTopmost and SetBottomMost static extension method for UIElement easily by adapting this code

User · Answer

This would require a sort  O n log n   but is very simple and flexible  Another advantage is being able to use it with LINQ to SQL   var maxObject   list OrderByDescending item   gt  item Height  First      Note that this has the advantage of enumerating the list sequence just once  While it might not matter if list is a List lt T gt  that doesn t change in the meantime  it could matter for arbitrary IEnumerable lt T gt  objects  Nothing guarantees that the sequence doesn t change in different enumerations so methods that are doing it multiple times can be dangerous  and inefficient  depending on the nature of the sequence   However  it s still a less than ideal solution for large sequences  I suggest writing your own MaxObject extension manually if you have a large set of items to be able to do it in one pass without sorting and other stuff whatsoever  O n     static class EnumerableExtensions       public static T MaxObject lt T U gt  this IEnumerable lt T gt  source  Func lt T U gt  selector        where U   IComparable lt U gt           if  source    null  throw new ArgumentNullException  source           bool first   true         T maxObj   default T          U maxKey   default U          foreach  var item in source               if  first                    maxObj   item                  maxKey   selector maxObj                   first   false               else                   U currentKey   selector item                   if  currentKey CompareTo maxKey   gt  0                        maxKey   currentKey                      maxObj   item                                                 if  first  throw new InvalidOperationException  Sequence is empty            return maxObj            and use it with   var maxObject   list MaxObject item   gt  item Height

[c#] How to perform .Max() on a property of all objects in a collection and return the object with maximum value

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