Calculating Mode

**Amberlampz** · 08-03-2011

Hello again. I'm looking to calculate a mode in an array, but I've run into a few problems with the syntax. I believe my general methodology would work well, though:

1. Go through the array
2. compare current index with the next index
3. up a counter each time they are equal
4. store each count value into a second array of pointers
5. find the largest value in the second array
6. print this value
7. print the value that the second array value points to

By all means, correct anything that's incorrect, improper or otherwise inefficient in the above. Here is my code snippet so far:

Code:

void hurrmode (int array[], int size)
{
	int i, j, *count, *array_two;

	for (i = 0; i < size; i++)
	{
		for (j = i + 1; j < size; j++)
		{
			if (array[i] == array[j])
			{
				count ++;
			}
		}
	}
}

I can't seem to figure out how to store the count values into a second array without getting a syntax error. I'm still not super familiar with the language, unfortunately.

**quzah** · 08-03-2011

You don't really need an array of pointers, just an array of numbers. *foo makes a pointer named foo, but it doesn't actually make it point to any memory. You could instead just do:

Code:

int foo[ HOWMANY ];

Initialize them all to 0 first, then increment whatever you need. I'm not really sure that's what you would want to be doing here, but that's how you would do what it is you think you should be doing.

Quzah.

**Amberlampz** · 08-03-2011

Thanks for the quick response. Hmmmm. I'm afraid I don't quite understand what you mean. I went ahead and changed some things around to make it simpler, though.

Code:

void hurrmode (int array[], int size)
{
	int i, j, k, count = 0, array_two[5], biggest = 0;

	for (i = 0; i < size; i++)
	{
		for (j = i + 1; j < size; j++)
		{
			if (array[i] == array[j])
			{
				count ++;
			}
			array_two[j] = count;
		}
	}

	for (k = 0; k < size; k++)
	{
		if (array_two[k] > biggest)
		{
			biggest = array_two[k];
		}
	}

	printf("Mode occurs %i times", biggest);
}

Okay, so this works (yes yes yes)! However, there are two things I would like to do with what I have right now. For starters, I want array_two to be of of size size, not 5. Secondly, I'd also like to print out the value of the mode in addition to just how often it occurs.

Would the second part require pointers, or would what you're saying work (I don't fully understand what you're saying, though)?

edit: corrected some mistakes, spelling, etc

**quzah** · 08-03-2011

Originally Posted by Amberlampz

For starters, I want array_two to be of of size size, not 5.

C99 will let you do that:

Code:

void foo( int size )
{
    int array[ size ];
}

Originally Posted by Amberlampz

Secondly, I'd also like to print out the value of the mode in addition to just how often it occurs.

Lets say we have an array and we want to print its contents, along with where they are in the array (because I don't know what you are asking exactly):

Code:

for( x = 0; x < size; x++ )
    printf( "array[ %d ] has %d for a value\n", x, array[ x ] );

Is that what you want to do?

Quzah.

**Amberlampz** · 08-03-2011

Originally Posted by quzah

C99 will let you do that:

Code:

void foo( int size )
{
    int array[ size ];
}

Unfortunately the compiler I'm using is Visual Studio 2010 (and they apparently have no plans to implement it). Is there a workaround, or would you suggest another compiler?

Originally Posted by quzah

Lets say we have an array and we want to print its contents, along with where they are in the array (because I don't know what you are asking exactly):

Code:

for( x = 0; x < size; x++ )
    printf( "array[ %d ] has %d for a value\n", x, array[ x ] );

Is that what you want to do?

Quzah.

Not quite. I'm looking to print out the value of the mode of an array and how many times that value occurs. I have the latter, but I'm not sure (syntactically) how to print out the value itself. Apologies if I wasn't clear about that.

I'm thinking that's going to require pointers, but I'm not sure.

**laserlight** · 08-03-2011

Originally Posted by Amberlampz

Is there a workaround

The "workaround" is actually the more common method: use dynamic memory allocation with say, malloc and free from <stdlib.h>.

**quzah** · 08-03-2011

Originally Posted by Amberlampz

Not quite. I'm looking to print out the value of the mode of an array and how many times that value occurs. I have the latter, but I'm not sure (syntactically) how to print out the value itself. Apologies if I wasn't clear about that.

I'm still not clear on what you can't figure out how to print.

Code:

int x = putsomevaluehere;
printf( "x is %d\n", x ); /* print whatever value x has */

So, assuming you actually have a value stored some place, or can figure out how to store it some place, you should be able to print that value out. So:

Code:

int data[] = { 1, 2, 3, 1, 1, 2, 5 }; /* <--- has v */
int mode[] = { 0, 3, 2, 1, 0, 1 }; /* 0 0s, 3 1s, 2 2s, etc... */
int x;
for( x = 0; x < 6; x++ ) /* because we happen to have six slots in our array */
    printf( "mode[ %d ] has the value of %d\n", x, mode[ x ] );

As I illustrated earlier.

Quzah.

**whiteflags** · 08-03-2011

Not quite. I'm looking to print out the value of the mode of an array and how many times that value occurs. I have the latter, but I'm not sure (syntactically) how to print out the value itself. Apologies if I wasn't clear about that.

Make it so the tally in array_two[2] means the values of 2 in array and so forth.

**Amberlampz** · 08-04-2011

Originally Posted by laserlight

The "workaround" is actually the more common method: use dynamic memory allocation with say, malloc and free from <stdlib.h>.

Noted, and thanks.

Originally Posted by quzah

I'm still not clear on what you can't figure out how to print.

Given any set of numbers stored in an array, I compare an array index with the one above it, and if they're equal I increment a counter. These counter values are then stored into a second array. What I would like is to print out the value of the number that corresponds to the highest counter.

The actual syntax of printing out the value (like how you gave an example) isn't the issue, but rather creating a variable that corresponds to the value is what's troubling me. My bad for not being super clear on that.

Originally Posted by whiteflags

Make it so the tally in array_two[2] means the values of 2 in array and so forth.

So make the tally a pointer referencing the array index?

I think I'm going to have to read up on pointers more if I go any further with this, provided it's the case that I do need to use pointers. Not familiar with them at all.

**AndrewHunter** · 08-04-2011

Originally Posted by Amberlampz

Hello again. I'm looking to calculate a mode in an array, but I've run into a few problems with the syntax. I believe my general methodology would work well, though:

1. Go through the array
2. compare current index with the next index
3. up a counter each time they are equal
4. store each count value into a second array of pointers why?
5. find the largest value in the second arraywhy?
6. print this value
7. print the value that the second array value points toYou don't need a second array

Ok, it seems we have gotten off track here. To go back to your original question - How to find the mode of an array. Correct? The mode, is simply the value in the array that occurs the most. That is it, there is no need for two arrays or pointers or anything like that. This really is a simple max problem. Something like:

Code:

#include <stdio.h>

#define ARRAYSIZE 10

int main(void){

	int myArray[ARRAYSIZE] = {8,3,4,5,2,3,2,2,7,2};
	int count=1, max=0, index=0;

	for(int i = 0; i < ARRAYSIZE;i++){
		for(int j = i+1; j < ARRAYSIZE;j++){
			if(myArray[i]==myArray[j])
				count++;
		}
		if(count > max){
			max = count;
			index = i;
		}
		count = 1;
	}

	printf("The mode of myArray is %d, and occurs %d times\n",myArray[index],max);
	getchar();
	return(0);
}

**quzah** · 08-04-2011

Originally Posted by Amberlampz

Given any set of numbers stored in an array, I compare an array index with the one above it, and if they're equal I increment a counter.

I'm not sure how this is giving you a mode. You are comparing array[ 1 ] with array[ 0 ] to see if they are the same? So basically all you are doing is looking for two consecutive numbers in an array? That's not mode as far as I know.

Originally Posted by Amberlampz

These counter values are then stored into a second array. What I would like is to print out the value of the number that corresponds to the highest counter.

I already showed you that.

Array 1 holds values of a bunch of data.
Array 2 holds values of indexes related to the first array.

Code:

index = array2[ somespot ];
printf( "array1[ index ] holds value of %d\n", index, array1[ index ] );

Quzah.

**AndrewHunter** · 08-04-2011

If the OP just wants to calculate the mode, e.g. "one of a range of values that has the highest frequency as determined statistically", there is no need for a second array. In fact this whole thing boils down to a simple max program as I pointed out above. However, I agree with you in that if the OP wants something else they need to be a lot more specific as to what they require.

I think the basic problem here is that the OP has no clue what they want, something of a norm around here unfortunately.

**Amberlampz** · 08-05-2011

Originally Posted by AndrewHunter

Ok, it seems we have gotten off track here. To go back to your original question - How to find the mode of an array. Correct? The mode, is simply the value in the array that occurs the most. That is it, there is no need for two arrays or pointers or anything like that. This really is a simple max problem. Something like:

<AndrewHunter's code>

Wow. It's almost hilarious how the simpler answers are the hardest to come by. After sleeping on it I deduced that pointers wouldn't really be needed unless I wanted to over-complicate things. Anyways, thanks. Code works! If it's any consolation, I've drawn out a flowchart on some paper to understand the process in addition to shamelessly jacking and adjusting your code.

Originally Posted by quzah

I'm not sure how this is giving you a mode. You are comparing array[ 1 ] with array[ 0 ] to see if they are the same? So basically all you are doing is looking for two consecutive numbers in an array? That's not mode as far as I know.I already showed you that.

Array 1 holds values of a bunch of data.
Array 2 holds values of indexes related to the first array.

Code:

index = array2[ somespot ];
printf( "array1[ index ] holds value of %d\n", index, array1[ index ] );

Quzah.

I guess I'm just not explaining it well enough. Forgive me, but my experience with C is pathetically small (one month and change) so I'm not completely up to speed with everything yet. I imagine it's like trying to glean information from a toddler (me) for you, so thanks for being patient regardless.

Originally Posted by AndrewHunter

If the OP just wants to calculate the mode, e.g. "one of a range of values that has the highest frequency as determined statistically", there is no need for a second array. In fact this whole thing boils down to a simple max program as I pointed out above. However, I agree with you in that if the OP wants something else they need to be a lot more specific as to what they require.

I think the basic problem here is that the OP has no clue what they want, something of a norm around here unfortunately.

Nope, nothing too specific. Just wanting to familiarize myself with the language. Unfortunately there seems to be a slight communication barrier between myself, who is very inexperienced, and you guys, who have obviously been doing this for a long time. You could chalk it up to inexperience, but hopefully that won't be the case in a couple of months after coding some more!

Thanks for the patience, especially Quzah. I know how frustrating it is to deal with somebody that can't even communicate information properly, so big kudos and I'll be thanking your posts.

Thread: Calculating Mode

Thread Tools

Search Thread

Display

Calculating Mode

Similar Threads

.Net C++ program runs fine in debug mode but not in normal mode?

what is this compile error , my code compiles fine in debug mode but not release mode

calculating the mode

Calculating mode

inverse mode and flash mode for text