CODEWITHSUNDEEP
javac#c#-3.0
Syamesh K
Syamesh K

Reputation: 826

How to check if a boolean value is true from a list of values

I have a list of boolean values, what is the most efficient way to check if one of the boolean is true and all others are false?

For example, I have a array of 100 boolean values, how can I check if 1 boolean is true and all other booleans are false.

Upvotes: 1

Views: 6758

Answers (9)

Syamesh K
Syamesh K

Reputation: 826

I used IEnumerable.Count(Func) from System.Linq, with T as bool

bool[] values = {true, false, false, false};
int trueCount = values.Count(b=> b);

This will you the number of 'true' values in the list

Upvotes: 0

Abinash
Abinash

Reputation: 481

In C# using LinQ you can do it in single line of code

var check = itemList.Any(x => x.isActive == true);

It Will return true if any one model is active in the list.

Upvotes: 1

Chandana Kumara
Chandana Kumara

Reputation: 2645

 int countTrue=0;
for(boolean value: [Your List]){
     if(value)
       countTrue++;      

     if(countTrue>1) 
     break;  
 }

Check countTrue==1 OR not

Upvotes: 0

Andy Turner
Andy Turner

Reputation: 140309

Iterate through the list and check each value. Stop if you find a second true value:

boolean found = false;
for (boolean b : list) {
  if (b) {
    if (found) return false;
    found = true;
  }
}
return found;

Alternatively, you can use List.indexOf and List.lastIndexOf:

int indexOfFirstTrue = list.indexOf(true);
return indexOfFirstTrue != -1 && list.lastIndexOf(true) != indexOfFirstTrue;

Upvotes: 1

smsnheck
smsnheck

Reputation: 1593

If you are working with Java 8 you can use this:

long size = booleanList.stream().filter(b -> Boolean.TRUE.equals(b)).count();
if(size == 1) {
    // do something
}

Upvotes: 0

Prashanth Debbadwar
Prashanth Debbadwar

Reputation: 1047

int countTrue=0;
for(boolean value: [Your List]){
 if(value){
   countTrue++;  
   if(countTrue>1){
     // true is more than one time
     break;
   } 
  }

}

Upvotes: 0

svarog
svarog

Reputation: 9839

Using Java 8 streams

List<Boolean> bools = list.stream().filter(val -> false)
            .collect(Collectors.asList());

if (bools.size()==99) { ...}

You filter out all the values that are true. if your list has 100 values, you will receive a new list with 99 false values.

If you know you have only 1 true value in your list you can stop when you find it.

list.stream().filter(val -> true)
            .findFirst()
            .get();

It will get the first true value it encounters and returns it inside an Optional

Upvotes: 0

progrAmmar
progrAmmar

Reputation: 2670

The author wants to know if only 1 value is Boolean

how can I check if 1 boolean is true and all other booleans are false.

in C# I would do something like

Suppose

List<bool> booleanList;

Then

int trueCount = booleanList.Count(b => b);
int falseCount = booleanList.Count(b => !b);

Upvotes: 2

devops
devops

Reputation: 9179

Most performant way is to use BitSet instead of array:

BitSet set = new BitSet(100); // ~ boolean[] array = new boolean[100];
set.set(42); // ~ array[42] = true;
[...]
int countTrueBits = set.cardinality();

BitSet uses shift operations, so it is very fast.

Read more: boolean[] vs. BitSet: Which is more efficient?

Upvotes: 1

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