Mode (Statistics)

[getout]

i have created a menu driven statistics program in which it calculates no. of items, mean, median, mode, variance, standard deviation.
I have written function for all but except mode. I am not getting idea how to add function for mode which will calculate the mode.
Take a look in my current code:

#include <stdio.h>
#include <math.h>
#define SIZE 25
float std_dev(float a[], int n);
float mean(float a[], int n);
float variance(float a[], int n);
int median(float a[], int n);
float mode(float a[], int n);

int main(void)
{
  int ch;
  float value[SIZE];
  int i;
  printf("\t\t\t\t****MAIN MENU****");
  printf("\n\t\t\t\t-----------------");
  printf("\n\t\t\t\t1. Calculate Number of Items");
  printf("\n\t\t\t\t2. Calculate Median");
  printf("\n\t\t\t\t3. Calculate Mode");
  printf("\n\t\t\t\t4. Calculate Mean");
  printf("\n\t\t\t\t5. Calculate Variance");
  printf("\n\t\t\t\t6. Calculate Standard Deviation\n");
  printf("\n\t\t\t\t7. Calculate ALL\n");
  printf("\n\t\t\t\t-----------------");
  printf("\n\n\t\t\tEnter your choice : ");
  scanf("%d", &ch);
  switch(ch)
    {
      case 1:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("Number of items : %d\n", i);
        break;
      
      case 2:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("\nMedian : %d\n",median(value,SIZE));
        break;
      
      case 3:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("\nMode : ");
        break;
        
      case 4:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("\nMean : %.3f\n",mean(value,SIZE));
        break;
      
      case 5:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("\nVariance : %.3f\n",variance(value,SIZE));
        break;
      
      case 6:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("\nStandard Deviation : %.3f\n",std_dev(value,SIZE));
        break;
      
      case 7:
        printf("Enter %d float values\n", SIZE);
        for(i=0; i<SIZE; i++)
          scanf("%f", &value[i]);
        printf("\n\nNumber of items : %d\nMedian : %d\nMode : \nMean : %.3f\nVariance : %.3f\nStandard Deviation : %.3f\n",i,median(value,SIZE),mean(value,SIZE),variance(value,SIZE),std_dev(value,SIZE));
      
      default:
        break;
    }
}

int median(float a[], int n)
{
  int i,j;
  float t,median;
  
  for(i=1; i<=n-1; i++)
  {
    for(j=1; j<n-i; j++)
    {
      if (a[j] <= a[j+1])
      {
        t=a[j];
        a[j]=a[j+1];
        a[j+1]=t;
      }
      else
      continue;
    }
  }
  for(i=1; i<=n; i++)
  printf("\n%f ",a[i]);
  if(n%2 == 0)
    median = (a[n/2] + a[n/2+1])/2.0;
  else
    median = a[n/2 + 1];
  
  return(median);
}

float mean(float a[], int n)
{
  int i;
  float sum = 0.0, mean;
  for(i=0; i<n; i++)
    sum = sum + a[i];
  mean = sum/((float)n);
  
  return(mean);
}

float variance(float a[], int n)
{
  int i;
  float sum = 0.0, mean, variance, sumsqr, deviation;
  for(i=0; i<n; i++)
    sum = sum + a[i];
  mean = sum/((float)n);
  for(i=1; i<=n; i++)
  {
    deviation = a[i] - mean;
    sumsqr += deviation*deviation;
  }
  variance = sumsqr/(float)n;
  
  return(variance);    
}

float std_dev(float a[], int n)
{
  int i;
  float sum = 0.0, mean, variance, sumsqr, deviation, std_deviation;
  for(i=0; i<n; i++)
    sum = sum + a[i];
  mean = sum/((float)n);
  for(i=1; i<=n; i++)
  {
    deviation = a[i] - mean;
    sumsqr += deviation*deviation;
  }
  variance = sumsqr/(float)n;
  std_deviation = sqrt(variance);
  
  return(std_deviation);
}

[vart]

As I remember - you should just sort the array and take the item that's index is SIZE/2

[getout]

No mode is the element which frequently occurs, for eg: 25 values input are 0,0,1,2,3,4,5,6,6,6,6,6,7,8,9,0,6,5,4,3,2,1,7,8,9

so the mode will be 6

Now how would be a function for this??

[Salem]

Use the qsort() function in stdlib.h
There are many examples of it being used on the board.

[vart]

1. sort array
2. scan array
3. for each new value found - count the number of occurencies (tiil the new value found)
4. if the count is bigger than the mod_count - replace the mode_value and mode_count
5. continue till the end of the array

[whiteflags]

I don't believe that sorting is a necessary step. At least, I've done it before in math class without putting a series in order.

But beyond that, vart has the right idea.

[vart]

I don't believe that sorting is a necessary step. At least, I've done it before in math class without putting a series in order.

But beyond that, vart has the right idea.

without sorting you need to store several pairs (value, count) during scanning the array.
Working with sorted array - you need only to store two pairs (mode_value, mode_count) and (curr_value, curr_count).

both approaches are possible, depending on the preferencies that are out the bounds of the algorithm itself

[QuestionC]

I don't believe that sorting is a necessary step. At least, I've done it before in math class without putting a series in order.

But beyond that, vart has the right idea.

One way or another, you end up sorting the array, or performing an equivalent amount of work.

If you just count the elements 'without sorting', then you have, for all intents and purposes, performed what is called a Count Sort.

[getout]

thx for the help, i have created the function for mode & it is working properly but when same amount of two numbers is entered it give only one value
for eg. if 8,8,8 & 7,7,7 is entered in input it only gives mode as 8 not 8 & 7 both
so requesting a little bit of editing which should be done on the function

@Salem, I am quite new to C so cant work out qsort() function,...I have searched the board but cant get satisfactory answer. so can u plz give me example regarding this question.

here is my mode function

float mode(float a[], int n)
{
  int i,j,count=0,num=0,max=0;
  float t,mode;

  for(i=1; i<=n-1; i++)
  {
    for(j=1; j<n-i; j++)
    {
      if (a[j] >= a[j+1])
      {
        t=a[j];
        a[j]=a[j+1];
        a[j+1]=t;
      }
      else
      continue;
    }
  }
  for(i=1; i<n-1; i++)
  {
    if(num!=a[i])
      {
      num=a[i];
      count=1;
      }
      else
      count++;
    if(count>max)
    {
      max=count;
      mode=num;
    }
  }
  return(mode);
}

[Salem]

Like http://cboard.cprogramming.com/showt...ighlight=qsort
just change the int* to float*

[ssharish2005]

for eg. if 8,8,8 & 7,7,7 is entered in input it only gives mode as 8 not 8 & 7 both
so requesting a little bit of editing which should be done on the function

1. Calculate the count of all occurrences of number and store them in an array.
2. Get the max value of that array
3. Check is there any array element which is equal to max
4. If so print all those corresponding values which reflects the count

ssharish2005