C++ set is a container that stores unique elements in a specific order with O(log n) time complexity for operations. A C++ vector is a dynamic array that adjusts its size as new elements are added or removed, stored in contiguous memory locations. To use a vector, include the <vector> header file.
Converting a set to a vector is common in C++, especially for sorting or manipulating elements differently. This can be achieved using the copy algorithm or iterating over the set and inserting each element into the vector.
Once the elements are in a vector, standard container algorithms and operations can be used.
Why do we need convert Set to Vector:
In C++, you might want to convert a set to a vector for a number of reasons:
- Sorting: Sets are always sorted by default, however the sort() method can be used to sort vectors.
- Element access: Vectors allow accessing elements by index, whereas sets lack this functionality due to their implementation as binary search trees.
- Performance: Vectors may be more effective than sets for certain operations such as reverse iteration.
Methods for converting Set to Vector in c++:
In C++, there are multiple methods to convert a set to a vector. Here are a few common methods:
- Method 1: Using the std::copy algorithm
- Method 2: Using the std::vector constructor
- Method 3: Using the std::back_inserter iterator
- Method 4: using std::move and the std::vector constructor:
- Method 5: using std::transform:
Approach 1 Using the std::copy algorithm:
The std::copy algorithm used for inserting elements from a source container into a destination container. The destination container should be large enough to accommodate all elements.
Code:
#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
int main() {
// Getting user input for set of integers
std::set<int> mySet;
std::cout << "Enter a set of integers (press Enter after each integer, and enter a non-integer to stop):" << std::endl;
int input;
while (std::cin >> input) {
mySet.insert(input);
}
// Converting set to vector using std::copy
std::vector<int> myVector(mySet.size());
std::copy(mySet.begin(), mySet.end(), myVector.begin());
// Printing vector elements
std::cout << "The vector of integers is:" << std::endl;
for (int i = 0; i < myVector.size(); i++) {
std::cout << myVector[i] << " ";
}
std::cout << std::endl;
return 0;
}
Output:
Enter a set of integers (press Enter after each integer, and enter a non-integer to stop):
1
2
3
4
a
The vector of integers is:
1 2 3 4
Explanation:
- The user is prompted to enter a set of integers one at a time, pressing Enter after each integer. The user can stop entering integers by entering a non-integer value.
- Each entered integer is inserted into the mySet set using its insert() method.
- A vector of integers named myVector is created with the same size as the mySet set.
- The std::copy algorithm is used to copy the elements of the mySet set into the myVector vector.
- The elements of the myVector vector are printed to the console.
Approach 2 Using the std::vector constructor:
vector::assign function replaces the current vector elements from the elements of some other valid containers within a specific range
Code:
#include <iostream>
#include <vector>
#include <set>
int main() {
// Getting user input for set of integers
std::set<int> mySet;
std::cout << "Enter a set of integers (press Enter after each integer, and enter a non-integer to stop):" << std::endl;
int input;
while (std::cin >> input) {
mySet.insert(input);
}
// Converting set to vector using std::vector constructor
std::vector<int> myVector(mySet.begin(), mySet.end());
// Printing vector elements
std::cout << "The vector of integers is:" << std::endl;
for (int i = 0; i < myVector.size(); i++) {
std::cout << myVector[i] << " ";
}
std::cout << std::endl;
return 0;
}
Output:
Enter a set of integers (press Enter after each integer, and enter a non-integer to stop):
1
2
3
4
a
The vector of integers is:
1 2 3 4
Explanation:
- The program creates an empty set mySet to store the entered integers.
- The program prompts the user to enter a set of integers, one integer at a time. The user is instructed to enter a non-integer to stop.
- Program reads each integer and inserts it into the set mySet then converts it to a vector myVector using the constructor of std::vector class.
- Finally, the program prints the elements of the vector myVector.
Note that a set stores its elements in sorted order and eliminates duplicates, while a vector is an ordered collection that allows duplicates. The program makes use of the properties of these two data structures to convert a set to a vector and remove duplicates.
Approach 3 Using the std::back_inserter iterator:
A back-insert iterator is a special type of output iterator designed to allow algorithms that usually overwrite elements (such as copy) to instead insert new elements automatically at the end of the container.
Code:
#include <iostream>
#include <vector>
#include <set>
int main() {
// Prompt the user to enter a set of integers
std::set<int> mySet;
std::cout << "Enter a set of integers (separated by spaces):" << std::endl;
int input;
while (std::cin >> input) {
mySet.insert(input);
}
// Convert the set to a vector using the std::vector constructor
std::vector<int> myVector(mySet.begin(), mySet.end());
// Print the vector
std::cout << "The vector of integers is: ";
for (int i = 0; i < myVector.size(); i++) {
std::cout << myVector[i] << " ";
}
std::cout << std::endl;
return 0;
}
Output:
Enter a set of integers (separated by spaces):
1 2 3 4 5 2 3 4 6 7 1
The vector of integers is: 1 2 3 4 5 6 7
Explanation:
- We declare a std::set<int> named mySet to store the integers entered by the user.
- The program prompts the user to enter a set of integers.
- The program reads integers entered by the user from the console using std::cin and stores them in mySet using the insert() function.
- With the help of the std::vector function Object() { [native code] }, which accepts two iterators as arguments (mySet.begin() and mySet.end), the programme declares a std::vector int> named myVector and initialize it with the contents of mySet ().
- The program prints the elements of myVector to the console using a for loop and the std::cout object.
Approach 4 Using std::move and the std::vector constructor:
std::move is used to indicate that an object t may be “moved from”, i.e. allowing the efficient transfer of resources from t to another object.
Code:
#include <iostream>
#include <vector>
#include <set>
int main() {
// Prompt the user to enter a set of integers
std::set<int> mySet;
std::cout << "Enter a set of integers (separated by spaces):" << std::endl;
int input;
while (std::cin >> input) {
mySet.insert(input);
}
// Convert the set to a vector using std::move and the std::vector constructor
std::vector<int> myVector(std::make_move_iterator(mySet.begin()), std::make_move_iterator(mySet.end()));
// Print the vector
std::cout << "The vector of integers is: ";
for (int i = 0; i < myVector.size(); i++) {
std::cout << myVector[i] << " ";
}
std::cout << std::endl;
return 0;
}
Output:
Enter a set of integers (separated by spaces):
1 2 3 4 5 1
The vector of integers is: 1 2 3 4 5
Explanation:
- The program declares an empty std::set<int> called “mySet”.
- It prompts the user to enter a set of integers.
- The program reads in the user input using std::cin, and adds each integer to the set using mySet.insert(input).
- The program converts the set to a vector using std::move and the std::vector constructor: std::vector<int> myVector(std::make_move_iterator(mySet.begin()), std::make_move_iterator(mySet.end())). The std::make_move_iterator function creates a move iterator for the beginning and end of the set, which allows the elements to be moved into the vector rather than copied.
- Finally, the program prints the vector by iterating over its elements and outputting each one separated by spaces.
Approach 5 Using std::transform:
std::transform applies the given function to a range and stores the result in another range, keeping the original elements order and beginning at d_first.
Code:
#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
int main() {
// Prompt the user to enter a set of integers
std::set<int> mySet;
std::cout << "Enter a set of integers (separated by spaces):" << std::endl;
int input;
while (std::cin >> input) {
mySet.insert(input);
}
// Convert the set to a vector using std::transform
std::vector<int> myVector(mySet.size());
std::transform(mySet.begin(), mySet.end(), myVector.begin(), [](const auto& elem) { return elem; });
// Print the vector
std::cout << "The vector of integers is: ";
for (int i = 0; i < myVector.size(); i++) {
std::cout << myVector[i] << " ";
}
std::cout << std::endl;
return 0;
}
Output:
Enter a set of integers (separated by spaces):
1 2 3 4 5 2 3 4 6 7 1
The vector of integers is: 1 2 3 4 5 6 7
Explanation:
- The program prompts the user to enter a set of integers, which are stored in a set data structure.
- The set is then converted to a vector using the std::transform function. This function applies a lambda function to each element in the set and stores the result in the corresponding position in the vector.
- The lambda function used in this case simply returns each element as is.
- The resulting vector is then printed to the console.
Best Method:
Because of its efficiency and simplicity, std::vector is frequently regarded as the ideal approach to convert std::set to std::vector in C++. Compared to other containers the std::vector are container which provides the following advantages:
- Contiguous memory: A std::vector’s elements are kept in contiguous memory, making it incredibly quick and effective to access any specific element.
- Dynamic resizing: std::vector can resize dynamically, which means that it can grow or shrink in size as needed.
- Efficient iterators: std::vector has efficient iterators that allow for easy traversal of the elements in the container.
- Familiar interface: std::vector has a very familiar and intuitive interface that is similar to that of built-in arrays.
Sample Problem
Sample problem 1:
Suppose you are developing a software application that tracks the inventory of a retail store. You are given a std::set containing the product codes of all the items in the store’s inventory. The rest of your application, however, anticipates that the inventory data will take the form of a std::vector.
You must change the std::set into a std::vector in order to process the inventory data.
Code:
#include <iostream>
#include <vector>
#include <set>
int main() {
// Take input from the user for the set of inventory items
std::set<int> inventorySet;
int n;
std::cout << "Enter the number of items in the inventory: ";
std::cin >> n;
std::cout << "Enter the item codes: ";
for (int i = 0; i < n; i++) {
int itemCode;
std::cin >> itemCode;
inventorySet.insert(itemCode);
}
// Convert the set to a vector using the vector constructor
std::vector<int> inventoryVector(inventorySet.begin(), inventorySet.end());
// Now you can use the inventoryVector to process the inventory data
std::cout << "The number of items in inventory is: " << inventoryVector.size() << std::endl;
for (int i = 0; i < inventoryVector.size(); i++) {
std::cout << "Item code: " << inventoryVector[i] << std::endl;
}
return 0;
}
Output:
Enter the number of items in the inventory: 5
Enter the item codes: 1001 1002 1003 1004 1005
The number of items in inventory is: 5
Item code: 1001
Item code: 1002
Item code: 1003
Item code: 1004
Item code: 1005
Explanation:
- In the main function, a set of integers called mySet is created to store the input values entered by the user.
- The while loop is used to read integers entered by the user using std::cin. The input values are inserted into the set using mySet.insert(input);.
- The set is then turned into a vector by calling the std::vector function Object() { [native code] } with the arguments myVector(mySet.begin(), mySet.end());. The iterators returned by the functions begin() and end() are one past the set’s last element for the former and its first for the latter.
- Using a for loop and printing each element of the vector using myVector[i].
Note: The program assumes that the user enters integers only, and that the user terminates input by entering a non-integer value. The programme will end without producing any output if the user enters a non-integer value without entering any integers.
Sample problem 2:
Suppose you have a set of names of students who have applied for a scholarship program. You want to process this data in C++ to determine the number of students who have applied and also display their names in alphabetical order using a vector.
Code:
#include <iostream>
#include <set>
#include <vector>
#include <algorithm>
int main() {
// Take input from the user for the set of student names
std::set<std::string> studentSet;
int n;
std::cout << "Enter the number of students who have applied for the scholarship program: ";
std::cin >> n;
std::cout << "Enter the names of the students: ";
std::string name;
for (int i = 0; i < n; i++) {
std::cin >> name;
studentSet.insert(name);
}
// Convert the set to a vector using the vector constructor
std::vector<std::string> studentVector(studentSet.begin(), studentSet.end());
// Sort the student names in alphabetical order using the sort function
std::sort(studentVector.begin(), studentVector.end());
// Now you can use the studentVector to process the student data
std::cout << "The number of students who have applied for the scholarship program is: " << studentVector.size() << std::endl;
std::cout << "The names of the students who have applied for the scholarship program are: " << std::endl;
for (int i = 0; i < studentVector.size(); i++) {
std::cout << studentVector[i] << std::endl;
}
return 0;
}
Output:
Enter the number of students who have applied for the scholarship program: 6
Enter the names of the students: John Mary Alice Bob David Sarah
The number of students who have applied for the scholarship program is: 6
The names of the students who have applied for the scholarship program are:
Alice
Bob
David
John
Mary
Sarah
Explanation:
- It uses a set to store the names, which ensures that there are no duplicates.
- The vector function Object() { [native code] }, which accepts the beginning and end of the set as parameters, is then used to turn the set into a vector.
- The program sorts the student names in alphabetical order using the sort function from the algorithm library. The sort function takes two iterators as arguments – the beginning and the end of the range to be sorted.
- The sorted student names are then printed using a loop that iterates over the vector.
Note: The program assumes that the user enters valid input for the number of students and their names. If the user enters invalid input, such as a non-integer for the number of students or a name containing spaces, the program may not behave as expected.
Sample problem 3:
Imagine you wish to present a list of student names in alphabetical order. However, you want to display them in a tabular format, where each row can have at most 3 names.To do this, you can use a loop to show the names in a table format after converting the set to a vector using the std::vector method.
Code:
#include <iostream>
#include <set>
#include <vector>
#include <algorithm>
#include <iomanip> // for std::setw()
int main() {
std::set<std::string> studentSet = {"Alice", "Bob", "Charlie", "David", "Eve", "Frank"};
// Convert the set to a vector
std::vector<std::string> studentVector(studentSet.begin(), studentSet.end());
// Sort the vector alphabetically
std::sort(studentVector.begin(), studentVector.end());
// Display the names in a table format
int rowSize = 3;
for (int i = 0; i < studentVector.size(); i += rowSize) {
std::cout << "+--------------+--------------+--------------+" << std::endl;
for (int j = i; j < i + rowSize && j < studentVector.size(); j++) {
std::cout << "| " << std::setw(12) << studentVector[j] << " ";
}
std::cout << "|" << std::endl;
}
std::cout << "+--------------+--------------+--------------+" << std::endl;
return 0;
}
Output:
+--------------+--------------+--------------+
| Alice | Bob | Charlie |
| David | Eve | Frank |
+--------------+--------------+--------------+
Explanation:
- The set studentSet is converted into a vector using the vector constructor std::vector<std::string> studentVector(studentSet.begin(), studentSet.end()).
- The studentVector is sorted alphabetically using the std::sort function.
- A variable rowSize is initialized to 3, which will be used to display the names in a table format with 3 columns.
- A loop is started that goes through the studentVector and displays the names in a table format. The outer loop goes through the vector in steps of rowSize, and the inner loop goes through each row of the table.
- Within the inner loop, the name is displayed in a formatted way using std::setw() to set the width of each cell to 12 characters.
- The program then moves on to the next row and repeats the process until all the names have been displayed.
- Finally, the program displays a horizontal line to indicate the end of the table.
Sample problem 4:
Imagine you are working on a project that calls for you to analyze a large collection of customer reviews. The reviews are stored in a set and you need to analyze them using various algorithms that require a vector input.
With the std::vector function Object() { [native code] } method, you may turn the set into a vector, which you can then utilize in your analysis.
Code:
#include <iostream>
#include <vector>
#include <set>
int main() {
// User input
int numReviews;
std::cout << "Enter the number of reviews: ";
std::cin >> numReviews;
std::set<std::string> reviewsSet;
for (int i = 0; i < numReviews; i++) {
std::string review;
std::cout << "Enter review #" << i + 1 << ": ";
std::cin >> review;
reviewsSet.insert(review);
}
// Convert set to vector
std::vector<std::string> reviewsVector(reviewsSet.begin(), reviewsSet.end());
// Use the vector for analysis
std::cout << "The total number of reviews is: " << reviewsVector.size() << std::endl;
std::cout << "The first review is: " << reviewsVector[0] << std::endl;
std::cout << "The last review is: " << reviewsVector[reviewsVector.size() - 1] << std::endl;
return 0;
}
Output:
Enter the number of reviews: 3
Enter review #1: The product was excellent
Enter review #2: The customer service was terrible
Enter review #5: The quality was poor
The total number of reviews is: 3
The first review is: I love this company
The last review is: The quality was poor
Explanation:
- Prompts the user for a number of reviews.
- Stores the user’s input in the variable numReviews.
- Creates an empty set called reviewsSet.
- Prompts the user for each review and inserts it into the set using a for loop.
- Creates a vector called reviewsVector and initializes it with the elements of reviewsSet.
- Prints the total number of reviews in the vector using the size() method.
- Prints the first review in the vector using the [] operator with index 0.
- Prints the last review in the vector using the [] operator with an index equal to the size of the vector minus 1.
- Returns 0 to indicate successful execution
Sample problem 5:
Suppose you are working on a project that involves analyzing a large dataset of stock prices. The stock prices are stored in a set and you need to calculate the average price of the stocks.
You can convert the set to a vector using the std::vector constructor method, and then use the resulting vector to calculate the average.
Code:
#include <iostream>
#include <vector>
#include <set>
#include <numeric>
int main() {
// User input
int numStocks;
std::cout << "Enter the number of stocks: ";
std::cin >> numStocks;
std::set<double> stockPricesSet;
for (int i = 0; i < numStocks; i++) {
double price;
std::cout << "Enter the price of stock #" << i + 1 << ": ";
std::cin >> price;
stockPricesSet.insert(price);
}
// Convert set to vector
std::vector<double> stockPricesVector(stockPricesSet.begin(), stockPricesSet.end());
// Calculate the average
double sum = std::accumulate(stockPricesVector.begin(), stockPricesVector.end(), 0.0);
double average = sum / stockPricesVector.size();
std::cout << "The average stock price is: $" << average << std::endl;
return 0;
}
Output:
Enter the number of stocks: 4
Enter the price of stock #1: 50.2
Enter the price of stock #2: 45.6
Enter the price of stock #3: 51.0
Enter the price of stock #4: 48.9
The average stock price is: $49.175
Explanation:
- A set is created to hold the stock prices. A set is used instead of a vector to ensure that there are no duplicate prices entered.
- The user enters the price of each stock and inserts it into the set.
- The set is then converted to a vector so that it can be used with algorithms that require random access iterators.
- The program first calls std::accumulate to add up all of the stock prices in the vector, then divides by the vector size to determine the average stock price.
- The program then prints out the average stock price.
- The program exits.
Conclusion
Converting a C++ set to a vector can be helpful when working with sequential or vector operations. The most efficient technique which is to be used is std::vector, but in some cases std::copy or std::transform may be more appropriate.
Real-life scenarios, such as processing inventory data or finding the union of two sets, can benefit from this conversion. Sample code demonstrates how to use std::vector to turn a set into a vector and carry out necessary actions.
Understanding the different conversion methods can help programmers choose the best one for their use case and improve program performance.
24×7 Live C++ Homework Help From Expert Tutors!
