Find multiple modes in an array

[TJW]

I tried to write a function to find the mode(s), but it didn't print out the correct mode(s). The code and example are as below. Thank you for your time.

void calMode(int array[], int size)
{
    int counter=1,
	max=0,
	mode=array[0],
	modeCounter=0,  	 //Array size.
	modeNumbers[modeCounter];//Create an array to hold the mode(s) 
    for(int pass=0; pass<size-1; pass++)
    {
        if(array[pass]==array[pass+1])
        {
            counter++;
            if(counter>max)
            {
                max=counter;
                mode=array[pass];
                modeNumbers[modeCounter]=array[pass];
        	modeCounter++;
            }
        }
        else
        {
            counter=1; 
        }
    }
    for(int x=0; x<modeCounter; x++)
    {
	cout << modeNumbers[x] << " ";
    }
}

The test case:
The numbers in ascending order are:
0 1 2 3 4 4 5 5 5 7 8 9
The mode is/are 4 5

[lastchance]

TJW wrote:

The numbers in ascending order are:
0 1 2 3 4 4 5 5 5 7 8 9
The mode is/are 4 5

I can assure you that the mode of those numbers is just 5.

You (attempt to) create an array with 0 elements on line 7. Use a vector, then it can expand to the number required.

[TJW]

Hi lastchance:
I attempt to create an array with the elements of 1 to many. It depends on the mode of each test case. The code I wrote could print out the multiple modes of arrays, but it failed to print out the single mode. Is there any way that I can print the correct mode(s) out in all situations? Thank you!

[lastchance]

The code that you wrote won't (or, at least, shouldn't) compile. So it certainly wouldn't calculate multiple modes correctly.

Use a vector to hold your modes. Then you can push_back() to expand and resize() to contract.

As I said in my previous post, you attempt to create a size-zero array on line 7 (since that is the size of modeCounter at the time) ... so how do you expect to put anything in it. Declaring a standard array with a size known only at runtime would also be illegal in standard c++ anyway, but that's the least of your problems.

[lastchance]

You can try a two-pass version; it's probably easier.

#include <iostream>
#include <vector>
#include <string>
using namespace std;

//======================================================================

template<typename T> vector<T> mode( const vector<T> &A )  // Assumption: A already sorted
{
   // Pass 1: find longest run
   int longestRun = 1, currentRun = 1;           // Corresponds to just A[0]
   for ( int i = 1; i < A.size(); i++ )
   {
      currentRun = ( A[i] == A[i-1] ? currentRun + 1 : 1 );
      if ( currentRun > longestRun ) longestRun = currentRun;
   }
   if ( longestRun == 1 ) return A;              // Conveniently also deals with A being empty

   // Pass 2: add anything with longest run to modes
   vector<T> result;
   currentRun = 1;
   for ( int i = 1; i < A.size(); i++ )
   {
      currentRun = ( A[i] == A[i-1] ? currentRun + 1 : 1 );
      if ( currentRun == longestRun ) result.push_back( A[i] );
   }
   return result;
}

//======================================================================

int main()
{
   vector< vector<int> > test = { {},
                                  { 1 },
                                  { 1, 2, 3, 4, 5 },
                                  { 1, 2, 2, 4, 4, 6, 8 },
                                  { 1, 2, 3, 4, 4, 5, 5, 5, 7, 8, 9 } };

// vector< vector<double> > test = { { 3.4, 4.5, 4.5, 6.0, 9.0 , 9.0, 11.0 },
//                                   { 1.0, 5.5, 5.5, 5.5, 7.3 } };

// vector< vector<string> > test = { { "bus", "car", "car", "car", "rocket", "train", "train", "train" } };

   for ( const auto &A : test )
   {
      cout << "Array: ";   for ( auto e : A         ) cout << e << ' ';
      cout << '\n';
      cout << "Modes: ";   for ( auto e : mode( A ) ) cout << e << ' ';
      cout << "\n\n";
   }
}

Array: 
Modes: 

Array: 1 
Modes: 1 

Array: 1 2 3 4 5 
Modes: 1 2 3 4 5 

Array: 1 2 2 4 4 6 8 
Modes: 2 4 

Array: 1 2 3 4 4 5 5 5 7 8 9 
Modes: 5 

[TJW]

My instructor didn't like us to use vector, so I had to try other ways.
Here is the code:

void calMode(int array[], int size)
{
    int counter=1,
	 max=0,
	 mode=array[0],
	 modeCounter=0,				//Array size.
	 modeNumbers[modeCounter];	//Create an array to hold the mode(s) 
    for(int pass=0; pass<size-1; pass++)
    {
        if(array[pass]==array[pass+1])
        {
            counter++;
            if(counter>max)
            {
                max=counter;
                mode=array[pass];
            }
            if(counter==max || modeNumbers[modeCounter]!=modeNumbers[modeCounter+1]) 
            {
        	modeNumbers[modeCounter]=array[pass];
        	modeCounter++;
	    }
        }
        else
        {
            counter=1; 
        }
    }
	if(modeCounter==0)
	{
	    for(int x=0; x<size; x++)
	    {
		cout << array[x] << " "; //If there is no mode, print out the whole array. (The modes are every number of the array.)
	    }
	}
	else
	{
	    for(int x=0; x<modeCounter; x++)
	    {
	 	cout << modeNumbers[x] << " ";
	    }	
	}
}

[lastchance]

	 modeCounter=0,				//Array size.
	 modeNumbers[modeCounter];	//Create an array to hold the mode(s) 

I give up. Yes, really. I give up.