# It seems i have an error with my array but i'm not sure why any comments appreciated.

• October 22nd, 2012, 07:32 PM
JoshKesner
It seems i have an error with my array but i'm not sure why any comments appreciated.
Here is my code in complete

Code Java:

```public class BenfordsLaw{   public static void main(String[] args){     System.out.print("Generating Benford Sequence with initial amount =" + 100); System.out.print(", growth rate =" + .1); System.out.println(", number of periods =" + 1000); double[] testBenfordArray = generateBenfordNumbers(100,.1,1000); double[] proportionTestBenfordArray = calculatingLeadingDigitProportions(testBenfordArray); for (int i = 0; i<10; i++) System.out.println("In calculating Leading Digit Proportions, digit " + i + " appears " + proportionTestBenfordArray[i] + " proportion of the time.");     double[] testRandomNumbersArray = BenfordSupportCode.generateRandomNumbers(1000); double[] proportionTestRandomNumbersArray = calculatingLeadingDigitProportions(testRandomNumbersArray); for (int i = 0; i<10; i++) System.out.println("In calculating Random Leading Digit Proportions, digit " + i + " appears " + proportionTestRandomNumbersArray[i] + " proportion of the time.");   double idealDistribution = calculateDistance(testBenfordArray, BenfordSupportCode.getBenfordProbabilities()); System.out.println("The ideal Benford distribution is" + idealDistribution); double randomDistribution = calculateDistance(testRandomNumbersArray, BenfordSupportCode.getBenfordProbabilities()); System.out.println("The random distribution is" + randomDistribution);         }   public static double[] generateBenfordNumbers(double initialAmount, double growthRate, int numberPeriods){   double[] arrayBenford;   //creates number of spots in the array equal to value of numberPeriods arrayBenford = new double[numberPeriods];   arrayBenford[0]=initialAmount;   //Adding values to the array for(int i=1;i<numberPeriods;i++){   arrayBenford[i]=arrayBenford[i-1]*(1+growthRate);   }   return arrayBenford;   }   public static double[] calculatingLeadingDigitProportions(double[] numbers){   double[] calculatedArray;   //Creates 10 spots in the array calculatedArray = new double[10];     for(int i=0;i<numbers.length;i++){   if((calculateLeadingDigit((int)numbers[i]))==0.0) calculatedArray[0]++; if((calculateLeadingDigit((int)numbers[i]))==1.0) calculatedArray[1]++; if((calculateLeadingDigit((int)numbers[i]))==2.0) calculatedArray[2]++; if((calculateLeadingDigit((int)numbers[i]))==3.0) calculatedArray[3]++; if((calculateLeadingDigit((int)numbers[i]))==4.0) calculatedArray[4]++; if((calculateLeadingDigit((int)numbers[i]))==5.0) calculatedArray[5]++; if((calculateLeadingDigit((int)numbers[i]))==6.0) calculatedArray[6]++; if((calculateLeadingDigit((int)numbers[i]))==7.0) calculatedArray[7]++; if((calculateLeadingDigit((int)numbers[i]))==8.0) calculatedArray[8]++; if((calculateLeadingDigit((int)numbers[i]))==9.0) calculatedArray[9]++;   }   for(int i=0;i<calculatedArray.length;i++){   calculatedArray[i] = (calculatedArray[i]/numbers.length);   }   return calculatedArray;   }   public static int calculateLeadingDigit(int number){     if (number == 0) return 0; else{ double bigNumber = Math.abs(number); while (bigNumber >= 10.0) bigNumber = bigNumber/10.0; int intBigNumber = (int) bigNumber; //cast bigNumber to be an int for the return statement   return intBigNumber; } }     public static double calculateDistance(double[] array1, double[] array2){ double euclideanDistance = 0.0; for(int i=0;i<array1.length;i++){ euclideanDistance = euclideanDistance + Math.pow((array1[i]-array2[i]), 2); } euclideanDistance = Math.sqrt(euclideanDistance); return euclideanDistance; } }                     import java.util.Random;   public class BenfordSupportCode { //this method returns an array of random integers public static double[] generateRandomNumbers(int count) { //Note FYI: if you want to get a different sequence each time, change the number 1 //below to something else. However, it will be easier to debug any issues you have //if you leave this consistant as you can then reproduce your errors consistantly. Random randGenerator = new Random(1);   double[] random = new double[count]; for (int i = 0; i < count; i++) { random[i] = randGenerator.nextInt(10000); }     return random; }   //this method returns an array of the benford probabilities public static double[] getBenfordProbabilities() { double[] benfordDistribution = {0, .301, .176, .125, .097, .079, .067, .058, .051, .046}; return benfordDistribution; } } public static void main(String[] args) { }```

When i run this it runs a few things and then i get the error:
java.lang.ArrayIndexOutOfBoundsException: 10
at BenfordsLaw.calculateDistance(BenfordsLaw.java:100 )
at BenfordsLaw.main(BenfordsLaw.java:18)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknow n Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Un known Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at edu.rice.cs.drjava.model.compiler.JavacCompiler.ru nCommand(JavacCompiler.java:272)
>

i realize it is telling me i have an issue with my array1 and array2 values but because in the assignment it notes to just assume that the array lengths are the same i figure the code should work. Any comments or way to resolve this issue would be greatly appreciated.
Thanks
• October 22nd, 2012, 07:55 PM
C++kingKnowledge
Re: It seems i have an error with my array but i'm not sure why any comments apprecia
for starters check your for loop inside generateBenfordNumbers... does that code compute for every element in the array or does it stop one short?
• October 23rd, 2012, 09:37 AM
Zaphod_b
Re: It seems i have an error with my array but i'm not sure why any comments apprecia
Quote:

Originally Posted by JoshKesner
...
i realize it is telling me i have an issue with my array1 and array2 values ...

What the heck is the calculateDistance supposed to be calculating? (Answer: The distance between two arrays of equal length.)

For what two arrays are you supposed to be calculating the distance?

Aren't you supposed to do something like the following:

• Call your generateBenfordNumbers method to create an array of 1000 points and then call your calculateProportions method to obtain an array of proportions. (Ten elements, right?)

• Calculate the distance between this array of proportions and the ten-element array returned by the BenfordSupportCode.getBenfordProbabilities method.

• Call the generateRandomNumbers method from the BenfordSupportCode class to create an array of 1000 points and call your calculateProportions method to obtain another array of proportions. (Ten elements, right?)

• Calculate the distance between this array of proportions and the ten-element array returned by the BenfordSuppordCode.getBenfordProbabilities method.

Or what?

I mean, that's what you have shown for which it makes sense to be calculating any kind of distance. Or so it seems to me.

Cheers!

Z