Question

I have a set of five boolean values. If more than one of these are true I want to excecute a particular function. What is the most elegant way you can think of that would allow me to check this condition in a single if() statement? Target language is C# but I’m interested in solutions in other languages as well (as long as we’re not talking about specific built-in functions).

One interesting option is to store the booleans in a byte, do a right shift and compare with the original byte. Something like if(myByte && (myByte >> 1)) But this would require converting the separate booleans to a byte (via a bitArray?) and that seems a bit (pun intended) clumsy… [edit]Sorry, that should have been if(myByte & (myByte - 1)) [/edit]

Note: This is of course very close to the classical ‘population count’, ‘sideways addition’ or ‘Hamming weight’ programming problem – but not quite the same. I don’t need to know how many of the bits are set, only if it is more than one. My hope is that there is a much simpler way to accomplish this.

Answer 1

How about

  if ((bool1? 1:0) + (bool2? 1:0) + (bool3? 1:0) +        (bool4? 1:0) + (bool5? 1:0) > 1)       // do something 

or a generalized method would be…

   public bool ExceedsThreshold(int threshold, IEnumerable<bool> bools)     {        int trueCnt = 0;        foreach(bool b in bools)           if (b && (++trueCnt > threshold))                return true;        return false;               }  

or using LINQ as suggested by other answers:

    public bool ExceedsThreshold(int threshold, IEnumerable<bool> bools)     { return bools.Count(b => b) > threshold; } 

EDIT (to add Joel Coehoorn suggestion: (in .Net 2.x and later)

    public void ExceedsThreshold<T>(int threshold,                        Action<T> action, T parameter,                        IEnumerable<bool> bools)     { if (ExceedsThreshold(threshold, bools)) action(parameter); } 

or in .Net 3.5 and later:

    public void ExceedsThreshold(int threshold,              Action action, IEnumerable<bool> bools)     { if (ExceedsThreshold(threshold, bools)) action(); } 

or as an extension to IEnumerable<bool>

  public static class IEnumerableExtensions   {       public static bool ExceedsThreshold<T>           (this IEnumerable<bool> bools, int threshold)       { return bools.Count(b => b) > threshold; }   } 

usage would then be:

  var bools = new [] {true, true, false, false, false, false, true};   if (bools.ExceedsThreshold(3))       // code to execute  ...