Bool list check if every item in list is false

Question

I have a List<bool> with lots of values. What is the most efficient way to check if every single item in the list equals false?

Answer 1

You can use Enumerable.Any it will find satisfy the condition on first match. As Habib rightly said better to use Any as Enumerable.All would return true for an Empty list of bool.

!lst.Any(c=> c == true); 

OR use Enumerable.All

lst.All(c=> c == false); 

Answer 2

A significantly faster solution, not mentioned here, is using Contains

if (!myList.Contains(true))     // Great success - all values false!  

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I have compared Contains against IEnumerable.Any and Contains returns faster. In my tests IEnumerable.All performed the same as IEnumerable.Any, perhaps a similar algorithm is used for both these functions under the hood. I also checked IEnumerable.Exists which performed better than IEnumerable.Any and IEnumerable.All, but was still slower than Contains.

Of a list of 10,000,000 bool entries (I also tried 0 and 1 entries, with similar results), I came up with the following metrics:

Elapsed via Any = 95ms

Elapsed via All = 88ms

Elapsed via Exists = 27ms

Elapsed via Contains = 17ms

Contains is ~5.59x faster than Any!

Tested with the following code:

// setup initial vars var myList = new List<bool>(); for (int x = 0; x < 10000000; x++)     myList.Add(false);    var containsAllFalse = false; Stopwatch sw = new Stopwatch();  // start test sw.Start(); containsAllFalse = !myList.Any(x => x); sw.Stop();  // get result for Any var timeAny = sw.ElapsedMilliseconds;  // reset variable state (just in case it affects anything) containsAllFalse = false;     // start test 2 sw.Restart(); containsAllFalse = myList.All(x => x == false); sw.Stop();  // get result for All var timeAll = sw.ElapsedMilliseconds;  // reset variable state (just in case it affects anything) containsAllFalse = false;     // start test 3 sw.Restart(); containsAllFalse = !myList.Exists(x => x == true); sw.Stop();  // get result for All var timeExists = sw.ElapsedMilliseconds;  // reset variable state (just in case it affects anything) containsAllFalse = false;     // start test 4 sw.Restart();    containsAllFalse = !myList.Contains(true);           sw.Stop();  // get result from Contains var timeContains = sw.ElapsedMilliseconds;  // print results var percentFaster = Math.Round((double)timeAny / timeContains, 2); Console.WriteLine("Elapsed via Any = {0}ms", timeAny); Console.WriteLine("Elapsed via All = {0}ms", timeAll); Console.WriteLine("Elapsed via Exists = {0}ms", timeExists); Console.WriteLine("Elapsed via Contains = {0}ms", timeContains); Console.WriteLine("Contains is ~{0}x faster than Any!", percentFaster); 

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Note this will only work with types where type can only have two states (i.e. it won't work variables of >2 states, such as Nullable<bool>)