Write a mode method in Java to find the most frequently occurring element in an array

Question

The question goes   Write a method called mode that returns the most frequently occurring element of an array of integers  Assume that the array has at least one element and that every element in the array has a value between 0 and 100 inclusive  Break ties by choosing the lower value  For example  if the array passed contains the values  27  15  15  11  27   your method should return 15   Hint  You may wish to look at the Tally program from earlier in this chapter to get an idea of how to solve this problem    Below is my code that almost works except for single-element arrays public  static  int  mode int    n            Arrays sort n                int count2   0      int count1   0      int pupular1  0      int popular2  0                for  int i   0  i  lt  n length  i                      pupular1   n i               count1   0       see edit                  for  int j   i   1  j  lt  n length  j                          if  pupular1    n j   count1                               if  count1  gt  count2                            popular2   pupular1                  count2   count1                             else if count1    count2                        popular2   Math min popular2  pupular1                            return popular2     Edit  finally figured it out  Changed count1   0  to count1   1  everything works now

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Here is my answer   public static int mode int   arr        int max   0      int maxFreq   0       Arrays sort arr       max   arr arr length-1        int   count   new int max   1        for  int i   0  i  lt  arr length  i              count arr i                  for  int i   0  i  lt  count length  i              if  count i   gt  maxFreq                maxFreq   count i                        for  int i   0  i  lt  count length  i              if  count i     maxFreq                return i                      return -1

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import java util HashMap   public class SmallestHighestRepeatedNumber       static int arr       9  4  5  9  2  9  1  2  8  1  1  7  7     public static void main String   args        int mode   mode arr       System out println mode      public static int mode int   array        HashMap lt Integer  Integer gt  hm   new HashMap lt Integer  Integer gt         int max   1      int temp   0       for  int i   0  i  lt  array length  i               if  hm get array i      null                 int count   hm get array i                count                hm put array i   count                if  count  gt  max    temp  gt  array i   amp  amp  count    max                    temp   array i                   max   count                          else             hm put array i   1             return temp

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check this   Brief Pick each element of array and compare it with all elements of the array  weather it is equal to the picked on or not      int popularity1   0    int popularity2   0    int popularity item  array item    Array contains integer value  Make it String if array contains string value    for int i  0 i lt array length i           array item   array i         for int j  0 j lt array length j               if array item    array j                popularity1                       if popularity1  gt   popularity2             popularity item   array item            popularity2   popularity1                popularity1   0           popularity item  contains the most repeted item in an array

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public int mode int   array        int mode   array 0       int maxCount   0      for  int i   0  i  lt  array length  i              int value   array i           int count   1          for  int j   0  j  lt  array length  j                  if  array j     value  count                if  count  gt  maxCount                    mode   value                  maxCount   count                                    return mode

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Here  I have coded using single loop  We are getting mode from a j-1  because localCount was recently updated when j was j-1  Also N is size of the array  amp  counts are initialized to 0             After sorting the array          i   0 j 0          while i  N  amp  amp  j  N               if ar i     ar j                    localCount                    j                              else                  i                    localCount   0                            if localCount  gt  globalCount                   globalCount   localCount                  mode   ar j-1

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I know that this question is from a while ago  but I wanted to add an answer that I believe expands upon the original question  The addendum to this question was to write the mode method without relying upon a preset range  in this case  0 through 100   I have written a version for mode that uses the range of values in the original array to generate the count array   public static int mode int   list           Initialize max and min value variable as first value of list     int maxValue   list 0        int minValue   list 0          Finds maximum and minimum values in list     for  int i   1  i  lt  list length  i              if  list i   gt  maxValue                maxValue   list i                      if  list i   lt  minValue                minValue   list i                          Initialize count array with  maxValue - minValue   1  elements       int   count   new int maxValue - minValue   1          Tally counts of values from list  store in array count     for  int i   0  i  lt  list length  i              count list i  - minValue       Increment counter index for current value of list i  - minValue              Find max value in count array     int max   count 0     Initialize max variable as first value of count      for  int i   1  i  lt  count length  i              if  count i   gt  max                max   count i                          Find first instance where max occurs in count array     for  int i   0  i  lt  count length  i              if  count i     max                return i   minValue    Returns index of count adjusted for min max list values - this is the mode value in list                     return -1    Only here to force compilation  never actually used

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Based on the answer from  codemania23 and the Java Docs for HashMap I wrote this code snipped and tests of a method that returns the most occurrent number in an array of numbers   import java util HashMap   public class Example        public int mostOcurrentNumber int   array            HashMap lt Integer  Integer gt  map   new HashMap lt  gt             int result   -1  max   1          for  int arrayItem   array                if  map putIfAbsent arrayItem  1     null                    int count   map get arrayItem    1                  map put arrayItem  count                   if  count  gt  max                        max   count                      result   arrayItem                                                     return result            Unit Tests  import org junit Test   import static junit framework Assert assertEquals   public class ExampleTest extends Example         Test     public void returnMinusOneWhenInputArrayIsEmpty   throws Exception           int   array   new int 0           assertEquals mostOcurrentNumber array   -1               Test     public void returnMinusOneWhenElementsUnique             int   array   new int   0  1  2  3  4  5  6  7  8  9           assertEquals -1  mostOcurrentNumber array                Test     public void returnOne   throws Exception           int   array   new int   0  1  0  0  1  1  1           assertEquals 1  mostOcurrentNumber array                Test     public void returnFirstMostOcurrentNumber   throws Exception           int   array   new int   0  1  0  1  0  0  1  1           assertEquals 0  mostOcurrentNumber array

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I would use this code  It includes an instancesOf function  and it runs through each number   public class MathFunctions    public static int mode final int   n        int maxKey   0      int maxCounts   0       for  int i   n            if  instancesOf i  n   gt  maxCounts                maxCounts   instancesOf i  n               maxKey   i                       return maxKey     public static int instancesOf int n  int   Array        int occurences   0      for  int j   Array            occurences    j    n   1   0            return occurences     public static void main  String   args          TODO Auto-generated method stub     System out println mode new int    100 200 2 300 300 300 500           I noticed that the code Gubatron posted doesn t work on my computer  it gave me an ArrayIndexOutOfBoundsException

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This is not the most fastest method around the block  but is fairly simple to understand if you don t wanna involve yourself in HashMaps and also want to avoid using 2 for loops for complexity issues          int mode int n  int   ar        int personalMax 1 totalMax 0 maxNum 0       for int i 0 i lt n-1 i                   if ar i   ar i 1                         personalMax                 if totalMax lt personalMax                                totalMax personalMax                  maxNum ar i                                       else                       personalMax 1                      return maxNum

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Arrays sort arr       int max 0 mode 0 count 0      for int i 0 i lt N i i count            count   1          for int j i 1  j lt N  j                  if arr i     arr j                   count                      if count gt max                max count              mode   arr i

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You should use a hashmap for such problems  it will take O n  time to enter each element into the hashmap and o 1  to retrieve the element  In the given code  I am basically taking a global max and comparing it with the value received on  get  from the hashmap  each time I am entering an element into it  have a look   hashmap has two parts  one is the key  the second is the value when you do a get operation on the key  its value is returned   public static int mode int   array        HashMap lt Integer Integer gt  hm   new HashMap lt Integer Integer gt         int max    1      int temp   0       for int i   0  i  lt  array length  i               if  hm get array i      null                 int count   hm get array i                count                hm put array i   count                if count  gt  max                    max    count                  temp   array i                                    else              hm put array i  1             return temp

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I have recently made a program that computes a few different stats  including mode  While the coding may be rudimentary  it works for any array of ints  and could be modified to be doubles  floats  etc  The modification to the array is based on deleting indexes in the array that are not the final mode value s   This allows you to show all modes  if there are multiple  as well as have the amount of occurrences  last item in modes array   The code below is the getMode method as well as the deleteValueIndex method needed to run this code  import java io File  import java util Scanner  import java io PrintStream   public static int   getMode final int   array                 int   numOfVals   new int array length     int   valsList   new int array length        initialize the numOfVals and valsList    for int ix   0  ix  lt  array length  ix           valsList ix    array ix          for int ix   0  ix  lt  numOfVals length  ix           numOfVals ix    1           freq table of items in valsList    for int ix   0  ix  lt  valsList length - 1  ix           for int ix2   ix   1  ix2  lt  valsList length  ix2              if valsList ix2     valsList ix                numOfVals ix     1                            deletes index from valsList and numOfVals if a duplicate is found in valsList    for int ix   0  ix  lt  valsList length - 1  ix              for int ix2   ix   1  ix2  lt  valsList length  ix2              if valsList ix2     valsList ix                valsList   deleteValIndex valsList  ix2              numOfVals   deleteValIndex numOfVals  ix2                             finds the highest occurence in numOfVals and sets it to most    int most   0     for int ix   0  ix  lt  valsList length  ix           if numOfVals ix   gt  most            most   numOfVals ix                   deletes index from valsList and numOfVals if corresponding index in numOfVals is less than most    for int ix   0  ix  lt  numOfVals length  ix           if numOfVals ix   lt  most            valsList   deleteValIndex valsList  ix           numOfVals   deleteValIndex numOfVals  ix           ix--                  sets modes equal to valsList  with the last index being most the highest occurence     int   modes   new int valsList length   1      for int ix   0  ix  lt  valsList length  ix           modes ix    valsList ix          modes modes length - 1    most     return modes      public static int   deleteValIndex int   array  final int index         int   temp   new int array length - 1     int tempix   0       checks if index is in array    if index  gt   array length         System out println  I m sorry  there are not that many items in this list          return array           deletes index if in array    for int ix   0  ix  lt  array length  ix           if ix    index            temp tempix    array ix           tempix                 return temp

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You should be able to do this in N operations  meaning in just one pass  O n  time   Use a map or int    if the problem is only for ints  to increment the counters  and also use a variable that keeps the key which has the max count seen  Everytime you increment a counter  ask what the value is and compare it to the key you used last  if the value is bigger update the key   public class Mode   public static int mode final int   n        int maxKey   0      int maxCounts   0       int   counts   new int n length        for  int i 0  i  lt  n length  i              counts n i              if  maxCounts  lt  counts n i                  maxCounts   counts n i                maxKey   n i                       return maxKey     public static void main String   args        int   n   new int     3 7 4 1 3 8 9 3 7 1        System out println mode n

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THIS CODE CALCULATES MODE  MEDIAN  AND MEAN  IT IS TESTED AND IT DOES WORK  It is a complete program from start to finish and will compile   import java util Arrays  import java util Random  import java math               author Mason     public class MODE       public static void main String args                  System out print  Enter the quantity of random numbers      gt  gt               int listSize   Expo enterInt            System out println            ArrayStats intStats   new ArrayStats listSize           intStats randomize            intStats computeMean            intStats computeMedian            intStats computeMode            intStats displayStats            System out println              class ArrayStats        private int list        private int size      private double mean              private double median            private int mode                  public ArrayStats int s   initializes class object               size   s          list   new int size              public void randomize                   This will provide same numbers every time    If you want to randomize this  you can         Random rand   new Random 555           for  int k   0  k  lt  size  k                list k    rand nextInt 11    10               public void computeMean                        double accumulator 0                 for  int index 0 index lt size index                   accumulator   list index                   mean   accumulator size                 public void computeMedian             Arrays sort list                   if  size 2  0                       median   list   size-1  2                    else if size  1 amp  amp size 2  0                                        double a   size  2-0 5                      int a2     int Math ceil a                       double b   size  2-0 5                      int b2    int Math floor b                       median    double  list a2  list b2   2                                    else if  size   1                      median   list 0                  public void computeMode          int popularity1   0    int popularity2   0    int array item    Array contains integer value  Make it String if array contains string value    for int i  0 i lt list length i           array item   list i         for int j  0 j lt list length j               if array item    list j                popularity1                   if popularity1  gt   popularity2             mode   array item            popularity2   popularity1                  popularity1   0            public void displayStats                 System out println Arrays toString list            System out println            System out println  Mean      mean           System out println  Median      median           System out println  Mode      mode           System out println

[java] Write a mode method in Java to find the most frequently occurring element in an array

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