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unique
Removes adjacent duplicates (elements that are equal to their predecessor)
Key Facts
Gyroscopic Couple: The rate of change of angular momentum (= Moment of Inertia.
= Angular velocity
= Angular velocity of precession.
Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.
Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.
Definition
The unique() algorithm is defined in the standard header <algorithm> and in the nonstandard backward-compatibility header <algo.h>.Interface
#include <algorithm> template < class ForwardIterator > ForwardIterator unique( ForwardIterator first, ForwardIterator last ); template < class ForwardIterator, class Predicate > ForwardIterator unique( ForwardIterator first, ForwardIterator last, Predicate comp );Parameters:
| Parameter | Description |
|---|---|
| first | A forward iterator addressing the position of the first element in the range to be scanned for duplicate removal |
| last | A forward iterator addressing the position one past the final element in the range to be scanned for duplicate removal |
| comp | User-defined predicate function object that defines the condition to be satisfied if two elements are to be taken as equivalent. A binary predicate takes two arguments and returns true when satisfied and false when not satisfied |
Description
Unique algorithm transforms a sequence such as each duplicate consecutive elements become a unique element. The first version usesoperator== to compare the elements, the second version uses the given binary predicate comp.Complexity
The complexity is linear; performs(last - first) - 1 applications of operator== (for the first version) or of comp (for the second version).References
Example:
Example - unique algorithm
Problem
This program illustrates the use of the STL unique() algorithm (default version) to remove adjacent duplicate copies of integer values from a vector of integers.
Workings
#include <iostream> #include <vector> #include <algorithm> using namespace std; int main() { int a1[] = {1, 2, 2, 3, 3, 6, 5, 2, 6, 9, 12, 2, 2, 2, 9, 10, 11, 12}; vector<int> v1(a1, a1+18); cout <<"\nHere are the values in the first vector:\n"; for (vector<int>::size_type i=0; i<v1.size(); i++) cout <<v1.at(i)<<" "; cout <<"\nNow we remove all adjacent duplicate copies of the " "\nvalues 2 and 3 and redisplay the values to confirm:\n"; vector<int>::iterator new_end = unique(v1.begin(), v1.end()); vector<int>::iterator p = v1.begin(); while (p != new_end) cout << *p++ << " "; int a2[] = {1, 1, 2, 2, 2, 3, 4, 5, 5, 5, 6, 7, 7, 8, 9, 10, 10, 10}; vector<int> v2(a2, a2+18); cout <<"\nHere are the values in the second vector:\n"; for (vector<int>::size_type i=0; i<v2.size(); i++) cout <<v2.at(i)<<" "; cout <<"\nNow we remove all adjacent duplicate copies of any " "\nof the values and redisplay the values to confirm:\n"; new_end = unique(v2.begin(), v2.end()); p = v2.begin(); while (p != new_end) cout <<*p++<<" "; return 0; }
Solution
Output:
Here are the values in the first vector:
1 2 2 3 3 6 5 2 6 9 12 2 2 2 9 10 11 12
Now we remove all adjacent duplicate copies of the
values 2 and 3 and redisplay the values to confirm: 1 2 3 6 5 2 6 9 12 2 9 10 11 12 Here are the values in the second vector: 1 1 2 2 2 3 4 5 5 5 6 7 7 8 9 10 10 10 Now we remove all adjacent duplicate copies of any
of the values and redisplay the values to confirm: 1 2 3 4 5 6 7 8 9 10
values 2 and 3 and redisplay the values to confirm: 1 2 3 6 5 2 6 9 12 2 9 10 11 12 Here are the values in the second vector: 1 1 2 2 2 3 4 5 5 5 6 7 7 8 9 10 10 10 Now we remove all adjacent duplicate copies of any
of the values and redisplay the values to confirm: 1 2 3 4 5 6 7 8 9 10
References