Multi Key Sort Problem
The multi-key sort problem involves sorting a collection of items based on multiple key values or attributes associated with each item.
For example, sorting a list of students by last name, first name, and age.
Java example:
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| // Student class
class Student {
String lastName;
String firstName;
int age;
}
public class MultiKeySort {
public static void sortStudents(List<Student> students) {
students.sort(Comparator.comparing(Student::getLastName)
.thenComparing(Student::getFirstName)
.thenComparingInt(Student::getAge));
}
}
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C++ example:
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| struct Student {
string lastName;
string firstName;
int age;
};
bool comp(Student a, Student b) {
if (a.lastName == b.lastName) {
if (a.firstName == b.firstName) {
return a.age < b.age;
}
return a.firstName < b.firstName;
}
return a.lastName < b.lastName;
}
void multiKeySort(vector<Student>& students) {
sort(students.begin(), students.end(), comp);
}
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Python example:
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| class Student:
def __init__(self, last, first, age):
self.last = last
self.first = first
self.age = age
def sort_students(students):
students.sort(key=lambda s: (s.last, s.first, s.age))
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Multi-key sorting allows controlling sort order by multiple attributes, rather than just a single key.
The multi key sort problem refers to sorting a collection of items based on multiple key values or attributes associated with each item. For example, sorting a list of students by last name and then first name requires a multi key sort.
Java example:
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| class Student {
String firstName;
String lastName;
int age;
// constructor and getters/setters
}
public class MultiKeySort {
public static void main(String[] args) {
List<Student> students = Arrays.asList(
new Student("John", "Doe", 18),
new Student("Jane", "Doe", 20),
new Student("Jack", "Smith", 22)
);
// Sort by last name, then first name
students.sort(Comparator.comparing(Student::getLastName)
.thenComparing(Student::getFirstName));
students.forEach(System.out::println);
}
}
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C++ example:
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| #include <algorithm>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
struct Student {
string firstName;
string lastName;
int age;
};
bool comp(Student a, Student b) {
if(a.lastName == b.lastName) {
return a.firstName < b.firstName;
}
return a.lastName < b.lastName;
}
int main() {
vector<Student> students = {
{"John", "Doe", 18},
{"Jane", "Doe", 20},
{"Jack", "Smith", 22}
};
sort(students.begin(), students.end(), comp);
for(auto s : students) {
cout << s.firstName << " " << s.lastName << "\n";
}
return 0;
}
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Python example:
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| class Student:
def __init__(self, first_name, last_name, age):
self.first_name = first_name
self.last_name = last_name
self.age = age
students = [
Student("John", "Doe", 18),
Student("Jane", "Doe", 20),
Student("Jack", "Smith", 22)
]
students.sort(key=lambda s: (s.last_name, s.first_name))
for s in students:
print(s.first_name, s.last_name)
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The key steps are:
Define a class to represent the items to sort with the necessary attributes
Implement a comparator function that first compares by one attribute, and uses the second attribute to break ties
Pass the custom comparator to the sorting algorithm to perform the multi-key sort
This allows sorting the items stably and efficiently by multiple keys.
The multi key sort problem involves sorting array elements based on multiple keys or attributes. For example, sorting employee records by last name and then first name.
It requires comparing objects on multiple keys in order, until an inequality is found or all keys are checked. Keys have a defined sort precedence order.
Multi key sorting is useful for sorting objects by multiple fields, like name, age, score etc. It provides flexible control over complex sorts.
Solution
Here is code to sort by last and first name:
Java
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| class Employee {
String lastName;
String firstName;
}
// Sort by last name, then first name
void multiKeySort(Employee[] employees) {
Arrays.sort(employees, new Comparator<Employee>() {
public int compare(Employee a, Employee b) {
int cmp = a.lastName.compareTo(b.lastName);
if (cmp != 0) return cmp;
return a.firstName.compareTo(b.firstName);
}
});
}
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C++
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| struct Employee {
string lastName;
string firstName;
};
// Sort by last name, then first name
bool comp(Employee a, Employee b) {
if (a.lastName == b.lastName) {
return a.firstName < b.firstName;
}
return a.lastName < b.lastName;
}
void multiKeySort(vector<Employee>& employees) {
sort(employees.begin(), employees.end(), comp);
}
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Python
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| class Employee:
def __init__(self, last, first):
self.last = last
self.first = first
# Sort by last name, then first name
def comp(emp1, emp2):
if emp1.last == emp2.last:
return emp1.first < emp2.first
return emp1.last < emp2.last
employees.sort(key=cmp_to_key(comp))
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Multi key sorting provides flexible control over complex sorts with precedence.
Description: Multi Key Sort Problem
The Multi Key Sort problem involves sorting a collection of items based on multiple attributes or keys. For example, you might need to sort a list of students first by grade level, then by name. The sorting process proceeds by first sorting on one key and then resolving ties by considering additional keys.
Solution:
Let’s consider a list of students, each with a name and a grade level. We’ll sort them first by grade level and then by name.
Java
In Java, you can use Collections.sort() with a custom comparator.
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| import java.util.*;
class Student {
String name;
int grade;
public Student(String name, int grade) {
this.name = name;
this.grade = grade;
}
}
public class MultiKeySort {
public static void main(String[] args) {
List<Student> students = new ArrayList<>();
students.add(new Student("Alice", 9));
students.add(new Student("Bob", 10));
students.add(new Student("Charlie", 9));
Collections.sort(students, new Comparator<Student>() {
public int compare(Student s1, Student s2) {
if (s1.grade != s2.grade) {
return s1.grade - s2.grade;
}
return s1.name.compareTo(s2.name);
}
});
}
}
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C++
In C++, you can use std::sort with a lambda function as the custom comparator.
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| #include <iostream>
#include <vector>
#include <algorithm>
struct Student {
std::string name;
int grade;
};
int main() {
std::vector<Student> students = {{"Alice", 9}, {"Bob", 10}, {"Charlie", 9}};
std::sort(students.begin(), students.end(), [](const Student &a, const Student &b) {
if (a.grade != b.grade) {
return a.grade < b.grade;
}
return a.name < b.name;
});
return 0;
}
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Python
In Python, you can use the sorted function with a custom key.
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| students = [
{'name': 'Alice', 'grade': 9},
{'name': 'Bob', 'grade': 10},
{'name': 'Charlie', 'grade': 9}
]
sorted_students = sorted(students, key=lambda x: (x['grade'], x['name']))
print(sorted_students)
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Key Takeaways:
- Multi Key Sort requires sorting data based on multiple attributes.
- Custom comparators can be used in Java and C++ to define complex sorting rules.
- Python’s
sorted function allows for straightforward sorting with multiple keys via its key argument. - The primary key is sorted first, followed by secondary keys to resolve ties.
By following these patterns, you can efficiently sort data based on multiple attributes.