How Can I Efficiently Remove Duplicates and Sort a Vector in C ?

Efficiently Eliminating Duplicates and Sorting a Vector

When handling large vectors with potential duplicates, it's crucial to find an efficient approach to both remove these duplicates and sort the vector. This article explores the most effective techniques for achieving this goal.

Using Vector Manipulation

One option is to use a combination of sort and unique operations on the vector. However, this method can prove inefficient due to the need to sort the entire vector before removing duplicates.

vec.erase(
  std::unique(vec.begin(), vec.end()),
  vec.end());
std::sort(vec.begin(), vec.end());

Converting to a Set

An alternative approach is to convert the vector to a set using a constructor or manually inserting elements. Sets automatically eliminate duplicates and provide sorted iteration. After conversion, the data can be copied back into a vector.

Manual Set Conversion

set<int> s;
unsigned size = vec.size();
for( unsigned i = 0; i < size; ++i ) s.insert( vec[i] );
vec.assign( s.begin(), s.end() );

Set Constructor Conversion

set<int> s( vec.begin(), vec.end() );
vec.assign( s.begin(), s.end() );

Performance Comparison

When the number of duplicates is large, converting to a set and dumping the data back into a vector becomes the faster option. Manually converting to a set also seems to be marginally faster than using the set constructor.

Optimal Sequence

For optimal performance, it's recommended to avoid sorting the vector before removing duplicates. By converting to a set and then transferring the data back, both tasks can be completed efficiently.

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