Finding the Mode of an ArrayList Java

Question

For the past few hours or so I've been trying to find the mode out of an ArrayList. In the program, you find the max, min, median, and mean as well. I've figured out all of those but I haven't been able to do the mode. I keep getting an IndexOutOfBoundsException. Here is my code so far:

public String getMode(){
  int mode = 0;
  int count = 0;

  for ( int i : file1 ){
    int x = file1.get(i);
    int tempCount = 1;

    for(int e : file1){
      int x2 = file1.get(e);

      if( x == x2)
        tempCount++;

      if( tempCount > count){
        count = tempCount;
        mode = x;
      }
    }
  }

  return ("The mode is " + mode);
}

The error I'm getting is:

java.lang.IndexOutOfBoundsException: Index: 181, Size: 108
at java.util.ArrayList.rangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at FunNumber2.getMode(FunNumber2.java:75)
at FunNumber2Tester.main(FunNumber2Tester.java:46)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

Sumit · Accepted Answer · 2013-12-27 22:37:58Z

2

This is your problem

for ( int i : file1 ){

change it to

for ( int i = 0; i< file1.size() ; i++ ){

This syntax

for ( int i : file1 ){

is giving you the iterated value of file1, meaning that if file1 = List([4,5,6]) then in the first iteration of the loop i == 4 not 0.

Obviously this would apply to the second loop as well.

Alternatively you could change

for ( int i : file1 ){
  int x = file1.get(i);

to

for ( int i : file1 ){
  int x = i;

And it would fix your problem. Hope that helps.

answered Dec 27, 2013 at 22:37

Sumit

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1 Comment

eagle Over a year ago

This did it! Thank you so much, I knew it was a simple solution but I couldn't find it. Thanks again!

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