Extracting mode from positive int vector

[hrxs1]

Hello everyone,
I have to create a program that gives out the mode, the number that appears the most ofen, of a vector with positive integers.
Actually, I tried something, but I didn't really get foward.
So, here is my code so far:

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <math.h>
#include <fstream>

using namespace std;

int mode(vector<int> s) //as i could'nt find a solution, i wanted at least to
                        //check whether i can write a 
                        //function that gives out the amount of the mode
{
	int z = 0;
	vector <int> mode; // store the amount of one integer in a new vector
	sort(s.begin(), s.end());
	int x = 0; 
	while (x<s.size()) 
	{ 
		if (x == 0) { ++x; }; //this should avoid out of range error
		if (s[x] - s[x - 1] == 0){ // are neighbouring ints equal?
			++z;
			++x; 
		}
		else if (s[x] - s[x - 1] != 0 && z > 0) {  //store z;
			mode.push_back(z);  
			z = 0; 
			++x; 
		} 
		else { 
			z = 0;
			++x; 
		} 
	} 
	sort(mode.begin(), mode.end()); 
	int i;
	for (i = 0; i<mode.size(); ++i);
	int m = mode[i]; //give out biggest value of mode vector
	return m;
} //i still get a vector subscript out of range error

int main() {
	vector <int> numbers;
	int max = 10;
	int y;
	cout << "Enter " << max << " integers!\n";
	for (int i = 0; i < max; ++i) {
		cin >> y;
		numbers.push_back(y);
	}
	sort(numbers.begin(), numbers.end()); //thought, this might be helpful
	for(int x = 0; x < max; ++x)
	cout << numbers[x] << endl;
	mode(numbers); 
	cin.get();
	return 0;
}

So yeah, I actually don't have much ideas now, so perhaps a hint would be enough in the first case.
And the assignment is actually to write a program that prints out the number of the mode, so my code isn't fullfilling the task at all, yet I thought, the mode-function could perhaps help me.

Thanks in advance,
hrxs1

[Naughty Albatross]

Hi,
Can you let us know full details of your assignment?

[Naughty Albatross]

> I have to create a program that gives out the mode, the number that appears the most often, of a vector with positive integers.

In other words, you want to write a program that prints out the number that repeats itself the most often in a vector with positive integers?

[Naughty Albatross]

Try this :

#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <fstream>

using namespace std;
int get_mode(vector<int> &v)
{
    map<int, int> m;
    for(int i = 0; i < v.size(); ++i) m[v[i]] = 0;
    for(int i = 0; i < v.size(); ++i)
    {
        m[v[i]] += 1;
    }
    int mode = 0;
    int num_mode = 0;
    for(map<int,int>::iterator it=m.begin(); it!=m.end(); ++it)
    {
       if(it->second > mode) { mode = it->second; num_mode = it->first; }
    }
   return num_mode;
}


int main()
{
	vector <int> numbers;
	int max = 10;
	int num, mode = 0;

	cout << "Enter " << max << " integers!\n";
	for (int i = 0; i < max; ++i) {
			cout << "Enter an integer : ";

		cin >> num;
		numbers.push_back(num);
	}

	for(int i = 0; i < max; ++i)
	cout << numbers[i] << endl;
	mode = get_mode(numbers);
	cout << "The mode number is : " << mode;
	cin.get();
	return 0;
}

[Naughty Albatross]

Does that help you? :)

[hrxs1]

Hello closed account,

Thank you for your reply. :-) I think this will help. It's a task from Stroustrup's book, Chapter 4.
I see, you use "maps", these aren't introduced in the chapter yet, so I will read about them and check whether I can understand your solution.

Best,
hrxs1

[Naughty Albatross]

Glad it helped :)

[Arslan7041]

Here's a slightly simpler method, not involving maps, and using only a single for-loop.

int getMode(std::vector<int>& vec)
{
    std::sort(vec.begin() , vec.end() ); // sort vector

    int mode = vec[0]; // set mode to first element of vector
    int occurrence = 1;        // its occurred once so far
    int maxOccurrence = 1;      // and maxOccurrence therefore is also 1


    for(int i = 1; i < vec.size(); i++)
    {
        // if we see a new number, set occurence to 1
        if(vec[i] > vec[i-1]){ occurrence = 1; }

        else occurrence++; // if same number, simply increment occurrence

// if occurrence is bigger than or equal to maxOccurrence, we found a new mode
        if(occurrence >= maxOccurrence) 
        {
            maxOccurrence = occurrence; // update maxOccurrence
            mode = vec[i]; // update mode
        }
    }

    return mode;
}

This takes advantage of a sorted vector (as you sort in the OP as well). Also keep in mind that if the vector contains multiple modes (i.e. different numbers that appear equally as frequently), this function will return the number greatest in value.

[Naughty Albatross]

@Arslan7041
+1

[hrxs1]

Thank you both, closed account & Arslan!

[Naughty Albatross]

Good to hear :)