Keep the duplicated values only - Vectors C++

Keep the duplicated values only - Vectors C++

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Assume I have a vector with the following elements {1, 1, 2, 3, 3, 4} I want to write a program with c++ code to remove the unique values and keep only the duplicated once. So the end result will be something like this {1,3}.

So far this is what I've done, but it takes a lot of time, Is there any way this can be more efficient,

vector <int> g1 = {1,1,2,3,3,4}
vector <int> g2;

for(int i = 0; i < g1.size(); i++)
{
  if(count(g1.begin(), g1.end(), g1[i]) > 1)
    g2.push_back(g1[i]);

}

v.erase(std::unique(g2.begin(), g2.end()), g2.end());

for(int i = 0; i < g2.size(); i++)
{
  cout << g2[i];
}

My approach is to create an <algorithm>-style template, and use an unordered_map to do the counting. This means you only iterate over the input list once, and the time complexity is O(n). It does use O(n) extra memory though, and isn't particularly cache-friendly. Also this does assume that the type in the input is hashable.

#include <algorithm>
#include <iostream>
#include <iterator>
#include <unordered_map>

template <typename InputIt, typename OutputIt>
OutputIt copy_duplicates(
        InputIt  first,
        InputIt  last,
        OutputIt d_first)
{
    std::unordered_map<typename std::iterator_traits<InputIt>::value_type,
                       std::size_t> seen;
    for ( ; first != last; ++first) {
        if ( 2 == ++seen[*first] ) {
            // only output on the second time of seeing a value
            *d_first = *first;
            ++d_first;
        }
    }
    return d_first;
}

int main()
{
    int i[] = {1, 2, 3, 1, 1, 3, 5}; // print 1, 3,
    //                  ^     ^
    copy_duplicates(std::begin(i), std::end(i),
                    std::ostream_iterator<int>(std::cout, ", "));
}

This can output to any kind of iterator. There are special iterators you can use that when written to will insert the value into a container.

std::unique in C++, It does not delete all the duplicate elements, but it removes duplicacy by just replacing Return Value: It returns an iterator to the element that follows the last element not removed. Displaying the vector after applying std::unique Become industry ready at a student-friendly price. My Personal Notes arrow_drop_up. Save  Python: Find duplicates in a list with frequency count & index positions; How to copy all Values from a Map to a Vector in C++; C++ : How to find an element in vector and get its index ? Python : 3 ways to check if there are duplicates in a List; Find frequency of each character in string and their indices | Finding duplicate characters in a string


Here's a way that's a little more cache friendly than unordered_map answer, but is O(n log n) instead of O(n), though it does not use any extra memory and does no allocations. Additionally, the overall multiplier is probably higher, in spite of it's cache friendliness.

#include <vector>
#include <algorithm>

void only_distinct_duplicates(::std::vector<int> &v)
{
    ::std::sort(v.begin(), v.end());
    auto output = v.begin();
    auto test = v.begin();
    auto run_start = v.begin();
    auto const end = v.end();
    for (auto test = v.begin(); test != end; ++test) {
       if (*test == *run_start) {
           if ((test - run_start) == 1) {
              *output = *run_start;
              ++output;
           }
       } else {
           run_start = test;
       }
    }
    v.erase(output, end);
}

I've tested this, and it works. If you want a generic version that should work on any type that vector can store:

template <typename T>
void only_distinct_duplicates(::std::vector<T> &v)
{
    ::std::sort(v.begin(), v.end());
    auto output = v.begin();
    auto test = v.begin();
    auto run_start = v.begin();
    auto const end = v.end();
    for (auto test = v.begin(); test != end; ++test) {
       if (*test != *run_start) {
           if ((test - run_start) > 1) {
              ::std::swap(*output, *run_start);
              ++output;
           }
           run_start = test;
       }
    }
    if ((end - run_start) > 1) {
        ::std::swap(*output, *run_start);
        ++output;
    }
    v.erase(output, end);
}

Determine Duplicate Elements, duplicated() determines which elements of a vector or data frame are duplicates all values can be compared, and may be the only value accepted for methods other bytes is allocated, setting nmax suitably can save large amounts of memory. x <- c(9:20, 1:5, 3:7, 0:8) ## extract unique elements (xu <- x[!​duplicated(x)])  In this post, we will see how to remove duplicates from a vector in C++. 1. std::remove. Simple solution is to iterate the vector and for each element, we delete all its duplicate from the vector if present. We can either write our own routine for this or use the std::remove algorithm that makes our code elegant.


Assuming the input vector is not sorted, the following will work and is generalized to support any vector with element type T. It will be more efficient than the other solutions proposed so far.

#include <algorithm>
#include <iostream>
#include <vector>

template<typename T>
void erase_unique_and_duplicates(std::vector<T>& v)
{
  auto first{v.begin()};
  std::sort(first, v.end());
  while (first != v.end()) {
    auto last{std::find_if(first, v.end(), [&](int i) { return i != *first; })};
    if (last - first > 1) {
      first = v.erase(first + 1, last);
    }
    else {
      first = v.erase(first);
    }
  }
}

int main(int argc, char** argv)
{
  std::vector<int> v{1, 2, 3, 4, 5, 2, 3, 4};
  erase_unique_and_duplicates(v);

  // The following will print '2 3 4'.
  for (int i : v) {
    std::cout << i << ' ';
  }
  std::cout << '\n';

  return 0;
}

duplicated function, duplicated() determines which elements of a vector or data frame are that all values can be compared, and may be the only value accepted for methods other than the default. Since a hash table of size 8*nmax bytes is allocated, setting nmax suitably can save large amounts of memory. x <- c(9:20, 1:5, 3:7, 0:8). i have a two columns table of 20k lines. 1st column: list of gene IDs (there can be duplicated IDs) 2nd column: a value What i want is to rank my list leaving with only unique gene IDs. For the duplicated gene IDs i want to leave only the ones with the highest score. here an example, Thanks in advance


Identify and Remove Duplicate Data in R, The R function duplicated() returns a logical vector where TRUE specifies which x <- c(1, 1, 4, 5, 4, 6) Following this way, you can remove duplicate rows from a data frame based on a column values, as follow: The function distinct() [dplyr package] can be used to keep only unique/distinct rows from a data frame. You can use std::sort first [1] . Then I would suggest you use std::unique [2] The code has been taken from the given link in the footnote [3] HEADERS REQUIRED > [code]&lt;algorithm&gt; [/code] CODE Note this is a sample code and you may have to make mi


I'll borrow a principal from Python which is excellent for such operations -

You can use a dictionary where the dictionary-key is the item in the vector and the dictionary-value is the count (start with 1 and increase by one every time you encounter a value that is already in the dictionary).

afterward, create a new vector (or clear the original) with only the dictionary keys that are larger than 1.

Look up in google - std::map

Hope this helps.

Unique values in array - MATLAB unique, If you only want one table variable to contain unique values, you can use the indices returned by unique Find the unique values of A and the index vectors ia and ic , such that C = A(ia) and A = C(ic) . Create a 10-by-3 matrix with some repeated rows. Find the unique elements of A , and preserve the legacy behavior. Output: 1 3 10 1 3 7 8 Here, in this vector, all the sub-groups having consecutive duplicate elements has been reduced to only one element. Note that it doesnot matter whether the same element is present later on as well, only duplicate elements present consecutively are handled by this function.


Remove duplicates from a vector in C++, std::unordered_set. The idea here is to iterate over the vector and keep track of visited elements in a set. If an element is not seen before, we  Solved: Hi Team, I found a code to get only duplicates using proc sort. But I need to get the duplicates with more variables ..example var1, var2,


R: Determine Duplicate Elements, Determines which elements of a vector or data frame are duplicates of Currently, FALSE is the only possible value, meaning that all values can be compared. x <- c(9:20, 1:5, 3:7, 0:8) ## extract unique elements (xu <- x[!​duplicated(x)])  The R function duplicated () returns a logical vector where TRUE specifies which elements of a vector or data frame are duplicates. Given the following vector: x <- c ( 1, 1, 4, 5, 4, 6) To find the position of duplicate elements in x, use this: duplicated (x) ## [1] FALSE TRUE FALSE FALSE TRUE FALSE. Extract duplicate elements:


Finding and removing duplicate records, You want to find and/or remove duplicate entries from a vector or data frame. value A 4 B 3 C 6 B 3 B 1 A 2 A 4 A 4 ') # Is each row a repeat? duplicated(df)