How to check if all list items have the same value and return it or return an otherValue if they don t

Question

If all the items in a list have the same value  then I need to use that value  otherwise I need to use an    otherValue     I can   t think of a simple and clear way of doing this  When the list is empty it should return the  quot other quot  value  See also Neat way to write loop that has special logic for the first item in a collection

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An alternative to using LINQ   var set   new HashSet lt int gt  values   return  1    set Count    values First     otherValue    I have found using HashSet lt T gt  is quicker for lists of up to   6 000 integers compared with   var value1   items First    return values All v   gt  v    value1    value1  otherValue

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public int GetResult List lt int gt  list   int first   list First    return list All x   gt  x    first    first   SOME OTHER VALUE

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This may be late  but an extension that works for value and reference types alike based on Eric s answer   public static partial class Extensions       public static Nullable lt T gt  Unanimous lt T gt  this IEnumerable lt Nullable lt T gt  gt  sequence  Nullable lt T gt  other  IEqualityComparer comparer   null   where T   struct  IComparable               object first   null          foreach var item in sequence                        if  first    null                  first   item              else if  comparer    null  amp  amp   comparer Equals first  item                   return other              else if   first Equals item                   return other                    return  Nullable lt T gt  first    other             public static T Unanimous lt T gt  this IEnumerable lt T gt  sequence  T other  IEqualityComparer comparer   null   where T   class  IComparable               object first   null          foreach var item in sequence                        if  first    null                  first   item              else if  comparer    null  amp  amp   comparer Equals first  item                   return other              else if   first Equals item                   return other                    return  T first    other

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return collection All i   gt  i    collection First            collection First     otherValue     Or if you re worried about executing First   for each element  which could be a valid performance concern    var first   collection First    return collection All i   gt  i    first    first   otherValue

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var val   yyy First   Value  return yyy All x  gt x Value    val    val   otherValue     Cleanest way I can think of  You can make it a one-liner by inlining val  but First   would be evaluated n times  doubling execution time   To incorporate the  empty set  behavior specified in the comments  you simply add one more line before the two above    if yyy    null     yyy Any    return otherValue

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Good quick test for all equal   collection Distinct   Count      1

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If a array is of type multidimension like below then we have to write below linq to check the data   example  here elements are 0 and i am checking all values are 0 or not  ip1          0 0 0 0         0 0 0 0         0 0 0 0         0 0 0 0        var value ip1 0  0      got the first index value     var equalValue   ip1 Any x  gt x Any xy  gt xy Equals         check with all elements value      if equalValue   returns true or false               return  Same Numbers          else        return  Different Numbers

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Though you certainly can build such a device out of existing sequence operators  I would in this case be inclined to write this one up as a custom sequence operator  Something like      Returns  other  if the list is empty     Returns  other  if the list is non-empty and there are two different elements     Returns the element of the list if it is non-empty and all elements are the same  public static int Unanimous this IEnumerable lt int gt  sequence  int other        int  first   null      foreach var item in sequence                if  first    null              first   item          else if  first Value    item              return other            return first    other      That s pretty clear  short  covers all the cases  and does not unnecessarily create extra iterations of the sequence   Making this into a generic method that works on IEnumerable lt T gt  is left as an exercise   -

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A slight variation on the above simplified approach   var result   yyy Distinct   Count      yyy Count

[c#] How to check if all list items have the same value and return it, or return an “otherValue” if they don’t?

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