how to know which boolean is true

Question

According to this thread Elegantly determine if more than one boolean is "true"

using this part of code...

public bool ExceedsThreshold(int threshold, IEnumerable<bool> bools)
{
   int trueCnt = 0;
   foreach(bool b in bools)
      if (b && (++trueCnt > threshold)) 
          ***//here i need to know which of b is the true***
          return true;
   return false;          
} 

I want to know which of bools variable is true?

Answer 1

If you want to know the indices of the true values, use the overload of Select that includes an index parameter:

IList<int> indices = bools.Select((b, i) => new {Index = i, IsTrue = b})
                          .Where(x => x.IsTrue)
                          .Select(x => x.Index)
                          .ToList();

Answer 2

Given a list of bool, this will return a list of the indexes that are true:

var myList = new List<bool>{false, false, true, true, false};

// Will return an IEnumerable containing {2, 3}:
var trueStuff = myList.Select((value, pos) => pos).Where(pos => myList[pos]);

Update: As pointed out in the comment below, the above would only work for a List, and not for an IEnumerable. I'll still leave it here though, as it may be useful in another similar situation.

Also, just for the record, here's a solution (albeit a slightly less elegant one) that should work in either case:

// Note: IEnumerable this time:
IEnumerable<bool> myList = new List<bool> { false, false, true, true, false };

var trueStuff = new List<int>();
int pos = 0;
foreach (var b in myList)
{
    if(b){ trueStuff.Add(pos); }
    pos++;
}

Answer 3

I want to know which of bools variable is true?

this one uses LINQ

IList<bool> _result = bools.Where(x => x == true);

Answer 4

I'm not sure if I am understanding this correctly, but if you wanted to know which Boolean values in an enumerated list are true and which ones are false, you could modify that routine to be something like this:

public static string GetBoolString(IEnumerable<bool> bools) 
{
  var boolArray = bools.ToArray();
  char[] data = new char[boolArray.Length];
  for (int i = 0; i < boolArray.Length; i++)
  {
    data[i] = boolArray[i] ? '1' : '0';
  }
  return new string(data);
}

Note that I am not presenting any "elegant" solution; just getting it done.

Answer 5

If you switch from IEnumerable to something with an inbuilt index (like an array or List), you can do this, to return a list of the indices that are true:

public IEnumerable<int> GetTrueIndices(bool[] b)
{
    return Enumerable.Range(0, b.Length).Where(i => b[i]);
}

with a list it would be this:

public IEnumerable<int> GetTrueIndices(List<bool> b)
{
    return Enumerable.Range(0, b.Count).Where(i => b[i]);
}

Answer 6

var firsttrue = bools.First(b => b);

Answer 7

Don't use IEnumerable if you want to work with indices, but use arrays.

To get indices use for loop and iterate over the array.