How to cast result of an operation on an int array to a double?

Question

I am iterating an int array to find the median, and then return the median, this portion of the program seems to work.

However, the median has to be cast to a double and it's showing the decimal place but it's not producing the correct output, why?

import java.util.*;

public class Example
{
    public static void main(String[] args)
    {
        int[] exampleArray = {2, 5, 10, 19, 23, 34};
        System.out.println("Median is: " + findMedian(exampleArray)); 
        // The output produced here should be 14.5 not 14.0
    }

    public static double findMedian(final int[] tempArray) 
    {
        int median = 0,
        Index = tempArray.length / 2;

        if(tempArray.length % 2 == 1)
        {
            median = tempArray[Index]; 

            /* I believe the problem is breaking down here I can't cast Index or 
               the tempArray to a double. I can copy the array elements into a new double array
               but I tried that as well and the output was still off. 
            */
        }       
        else 
            median = (tempArray[Index] + tempArray[Index - 1]) / 2; 

       return (double)median; 
    }   
}

Ryan Kozierok · Accepted Answer · 2016-03-15 19:58:35Z

1

As you suspected, your issue lies in the line

median = (tempArray[Index] + tempArray[Index - 1]) / 2;

This line is doing integer division. Integer division is what happens when you divide an integer by another integer, and it floors the result, so 5/2 is 2, even though 5.0/2.0 is 2.5.

You need a line like

double preciseMedian = (tempArray[Index] + tempArray[Index - 1]) / 2.0;

The decimal point makes the 2.0 a double, and that makes the entire division happen with the decimal place. Then you need to store it in variable that is a double because you won't be able to put it in an int.

answered Mar 15, 2016 at 19:58

Ryan Kozierok

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1 Comment

suroh Over a year ago

Ha, I didn't even consider that but it makes sense Thank you for the response and the explanation!

Rishi · Accepted Answer · 2016-03-15 19:57:35Z

0

The problem is that you have declared median to be int and performing calculations on int and storing it back to int. Now precision is lost and it is then converted to double which has doesn't regain precision , so change these parts of code.

   double median = 0;     
    median = ((double)tempArray[Index] + (double)tempArray[Index - 1]) / 2;

answered Mar 15, 2016 at 19:57

Rishi

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Comments

Andreas Brunnet · Accepted Answer · 2016-03-15 20:01:54Z

0

You might change your data type of median to double and ensure you are doing a division of a double value like so:

double median = 0;

Index = tempArray.length / 2;

if(tempArray.length % 2 == 1)
{
   median = tempArray[Index]; 
}       
else 
{
    /* You're having an integer division here. That means it's just
    cutting off the digits. A later cast from int to double would do 
    nothing. There were no digits before. 
    */
    median = (double)(tempArray[Index] + tempArray[Index - 1]) / 2; 
}
    return median; 
}

answered Mar 15, 2016 at 20:01

Andreas Brunnet

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Comments

Konstantins Bogdanovs · Accepted Answer · 2016-03-15 20:02:03Z

0

Your Index should be int.

double median = 0;
int Index = tempArray.length / 2; //should be int

if(tempArray.length % 2 == 1)
{
   median = tempArray[Index]; 

  /* I believe the problem is breaking down here I can't cast Index or 
     the tempArray to a double. I can copy the array elements into a new double array
     but I tried that as well and the output was still off. 
 */
}       
else 
   median = (tempArray[Index] + tempArray[Index - 1]) / 2.0;

edited Mar 15, 2016 at 20:02

answered Mar 15, 2016 at 19:55

Konstantins Bogdanovs

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1 Comment

suroh Over a year ago

Awesome! Thanks for that :)

Luke Melaia · Accepted Answer · 2016-03-15 20:02:38Z

0

Your problem is this line of code: median = (tempArray[Index] + tempArray[Index - 1]) / 2;.

Your median variable is an int, and you're trying to assign a double to it, so java is just going to remove the floating part of the expression and give you an int.

This line: return (double)median; is returning your integer variable (which is the median variable with the floating point removed) as a double, so it's not returning the double, but rather an integer with a floating point (.0).

The solution:

Change int median = 0; to double median = 0.0;. This will keep the floating point.

answered Mar 15, 2016 at 20:02

Luke Melaia

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Comments

Nikhil Gattani · Accepted Answer · 2016-03-15 20:03:02Z

0

Try by declaring median as double.

double median =0;

answered Mar 15, 2016 at 20:03

Nikhil Gattani

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Comments

Elliott Frisch · Accepted Answer · 2016-03-15 20:06:28Z

0

In Java 8+, you might use IntSummaryStatistics like

System.out.println(IntStream.of(exampleArray).summaryStatistics().getAverage());

In earlier versions of Java, the easiest solution I see would be to sum the elements and then divide the total by the count of elements (which is the median) like

public static double findMedian(final int[] tempArray) {
    long total = 0;
    for (int val : tempArray) {
        total += val;
    }
    return (double) total / tempArray.length;
}

answered Mar 15, 2016 at 20:06

Elliott Frisch

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