Welcome to our exploration of Compound Data Structures in C++. Having navigated through basic data structures, we'll delve into nested maps and vectors. These structures enable us to handle complex and hierarchical data, which is typical in real-world scenarios. This lesson will guide you through a recap of the basics, the creation and modification of nested maps and vectors, as well as common operations.
As a quick recap, std::vector is a dynamic array, while std::map is an associative container that stores key-value pairs. These structures can be nested. Here's a simple example of a school directory:
C++1#include <iostream> 2#include <vector> 3#include <map> 4#include <string> 5 6int main() { 7 // Map with grades as keys and vectors of students as values 8 std::map<std::string, std::vector<std::string>> school_directory = { 9 {"Grade1", {"Amy", "Bobby", "Charlie"}}, 10 {"Grade2", {"David", "Eve", "Frank"}}, 11 {"Grade3", {"George", "Hannah", "Ivy"}} 12 }; 13 14 // Prints the Grade1 list in the map 15 for (const auto& student : school_directory["Grade1"]) { 16 std::cout << student << " "; 17 } // Output: Amy Bobby Charlie 18 19 return 0; 20}
Just like their non-nested versions, creating nested structures is straightforward.
Nested Map:
C++1#include <iostream> 2#include <map> 3#include <string> 4 5int main() { 6 // Map within a map 7 std::map<std::string, std::map<std::string, std::string>> nested_map = { 8 {"fruit", { 9 {"apple", "red"}, // key-value pair within the 'fruit' map 10 {"banana", "yellow"} // another key-value pair within the 'fruit' map 11 }}, 12 {"vegetable", { 13 {"carrot", "orange"}, 14 {"spinach", "green"} 15 }} 16 }; 17 18 // Prints the nested map 19 for (const auto& category : nested_map) { 20 std::cout << category.first << ": "; 21 for (const auto& item : category.second) { 22 std::cout << item.first << "(" << item.second << ") "; 23 } 24 std::cout << std::endl; 25 } 26 27 return 0; 28}
Nested Vector:
C++1#include <iostream> 2#include <vector> 3 4int main() { 5 // Vectors within a vector 6 std::vector<std::vector<int>> nested_vector = { 7 {1, 2, 3}, // inner vector within the outer vector 8 {4, 5, 6}, // another inner vector within the outer vector 9 {7, 8, 9} // third inner vector within the outer vector 10 }; 11 12 // Prints the nested vector 13 for (const auto& vec : nested_vector) { 14 for (int val : vec) { 15 std::cout << val << " "; 16 } 17 std::cout << std::endl; 18 } 19 20 return 0; 21}
Nested Maps and Vectors:
C++1#include <iostream> 2#include <map> 3#include <vector> 4#include <string> 5 6int main() { 7 // Vectors within a map 8 std::map<std::string, std::vector<int>> map_of_vectors = { 9 {"numbers", {1, 2, 3}}, // keys associated with vectors 10 {"more_numbers", {4, 5, 6}} 11 }; 12 13 // Prints the map of vectors 14 for (const auto& item : map_of_vectors) { 15 std::cout << item.first << ": "; 16 for (int val : item.second) { 17 std::cout << val << " "; 18 } 19 std::cout << std::endl; 20 } 21 22 return 0; 23}
The retrieval of values from nested maps or vectors follows rules similar to those for their non-nested counterparts.
From Nested Map:
C++1#include <iostream> 2#include <map> 3#include <string> 4 5int main() { 6 // Map within a map 7 std::map<std::string, std::map<std::string, std::string>> nested_map = { 8 {"fruit", { 9 {"apple", "red"}, // key-value pair within the 'fruit' map 10 {"banana", "yellow"} // another key-value pair within the 'fruit' map 11 }}, 12 {"vegetable", { 13 {"carrot", "orange"}, 14 {"spinach", "green"} 15 }} 16 }; 17 18 // Accessing apple's color from nested map 19 std::cout << nested_map["fruit"]["apple"] << std::endl; // Output: red 20 21 return 0; 22}
From Nested Vector:
C++1#include <iostream> 2#include <vector> 3 4int main() { 5 // Vectors within a vector 6 std::vector<std::vector<int>> nested_vector = { 7 {1, 2, 3}, // inner vector within the outer vector 8 {4, 5, 6}, // another inner vector within the outer vector 9 {7, 8, 9} // third inner vector within the outer vector 10 }; 11 12 // Accessing the 3rd value from the 2nd vector in nested vector 13 std::cout << nested_vector[1][2] << std::endl; // Output: 6 14 15 return 0; 16}
From Both:
C++1#include <iostream> 2#include <map> 3#include <vector> 4#include <string> 5 6int main() { 7 // Vectors within a map 8 std::map<std::string, std::vector<int>> map_of_vectors = { 9 {"numbers", {1, 2, 3}}, // keys associated with vectors 10 {"more_numbers", {4, 5, 6}} 11 }; 12 13 // Accessing the second value from the 'numbers' vector in map_of_vectors 14 std::cout << map_of_vectors["numbers"][1] << std::endl; // Output: 2 15 16 return 0; 17}
The modification of nested vectors and maps is similar to that of non-nested versions.
Operations on Nested Maps:
C++1#include <iostream> 2#include <map> 3#include <string> 4 5int main() { 6 // Map within a map 7 std::map<std::string, std::map<std::string, std::string>> nested_map = { 8 {"fruit", { 9 {"apple", "red"}, 10 {"banana", "yellow"} 11 }}, 12 {"vegetable", { 13 {"carrot", "orange"}, 14 {"spinach", "green"} 15 }} 16 }; 17 18 // Modifying spinach's color to red 19 nested_map["vegetable"]["spinach"] = "red"; 20 21 // Adding cherry to the 'fruit' map in nested_map 22 nested_map["fruit"]["cherry"] = "red"; 23 24 // Deleting apple from the 'fruit' map in nested_map 25 nested_map["fruit"].erase("apple"); 26 27 return 0; 28}
Operations on Nested Vectors:
C++1#include <iostream> 2#include <vector> 3 4int main() { 5 // Vectors within a vector 6 std::vector<std::vector<int>> nested_vector = { 7 {1, 2, 3}, 8 {4, 5, 6}, 9 {7, 8, 9} 10 }; 11 12 // Adding 10 to the first vector in nested vector 13 nested_vector[0].push_back(10); 14 15 // Deleting the 2nd value from the 3rd vector in nested vector 16 nested_vector[2].erase(nested_vector[2].begin() + 1); 17 18 return 0; 19}
Bravo! You've made a journey through nested vectors and maps, terms that are becoming increasingly common in the data-intensive programming world. We've learned how to create, access, and modify values in these complex structures.
Up next, we have hands-on practice sessions to solidify your understanding of these concepts. Hold on to your hats!