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The C++ std::unordered_set::load_factor() function is used to return the load factor of the unordered_set container or the average number of element per bucket. The load factor is the ratio between the number of elements in the unordered_set and the number of buckets.

The load factor is calculated as follows −

load_factor = us.size() / us.bucket_count()

The load factor will displays 0, if the unordered_set contains 0 elements.

Syntax

Following is the syntax of std::unordered_set::load_factor() function.

float load_factor() const noexcept;

Parameters

This function does not accepts any parameter.

Return Value

This function returns the current load factor.

Example 1

Consider the following example, where we are going to demonstrate the usage of unordered_set::load_factor() function.

#include <iostream>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<int> uSet;
   cout << "size = " << uSet.size() << endl;
   cout << "bucket_count = " << uSet.bucket_count() << endl;
  
   cout << "load_factor = " << uSet.load_factor() << endl;  //load_factor
   cout << "max_load_factor = " << uSet.max_load_factor() << endl;
   return 0;
}

Output

If we run the above code it will generate the following output −

size = 0
bucket_count = 1
load_factor = 0
max_load_factor = 1

Example 2

In the following example, we are going to count the load_factor of the unordered_set.

#include <iostream>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<int> uSet = {10, 20, 30, 40};
   cout << "size = " << uSet.size() << endl; //Size of unordered set
   
   cout << "load_factor = " << uSet.load_factor() << endl;  //load_factor
   return 0;
}

Output

Following is the output of the above code −

size = 4
load_factor = 0.307692

Example 3

Let's look at the following example, where we are going to calculate the load_factor of the current unordered_set by using the formula.

#include <iostream>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<int> uSet = {10, 20, 30, 40, 50};
   float size = uSet.size();
   float bucket_count = uSet.bucket_count();
  
   cout << "size = " << size << endl; //Size of unordered set
   cout << "Bucket Count = " << bucket_count << endl; //Bucket count
   
   float load_factor = size/bucket_count;
   
   cout << "load_factor calculated by formula = " << load_factor << endl;  //load_factor
   return 0;
}

Output

Output of the above code is as follows −

size = 5
Bucket Count = 13
load_factor calculated by formula = 0.384615