How to calculate mean median mode and range from a set of numbers

Question

Are there any functions  as part of a math library  which will calculate mean  median  mode and range from a set of numbers

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public class Mode       public static void main String   args            int   unsortedArr   new int     3  1  5  2  4  1  3  4  3  2  1  3  4  1  -1 -1 -1 -1 -1           Map lt Integer  Integer gt  countMap   new HashMap lt Integer  Integer gt              for  int i   0  i  lt  unsortedArr length  i                  Integer value   countMap get unsortedArr i                 if  value    null                    countMap put unsortedArr i   0                 else                   int intval   value intValue                    intval                    countMap put unsortedArr i   intval                                    System out println countMap toString              int max   getMaxFreq countMap values             List lt Integer gt  modes   new ArrayList lt Integer gt              for  Entry lt Integer  Integer gt  entry   countMap entrySet                  int value   entry getValue                if  value    max                  modes add entry getKey                       System out println modes              public static int getMaxFreq Collection lt Integer gt  valueSet            int max   0          boolean setFirstTime   false           for  Iterator iterator   valueSet iterator    iterator hasNext                   Integer integer    Integer  iterator next                 if   setFirstTime                    max   integer                  setFirstTime   true                            if  max  lt  integer                    max   integer                                  return max            Test data        Modes  1 3  for   3  1  5  2  4  1  3  4  3  2  1  3  4  1      Modes  -1  for   3  1  5  2  4  1  3  4  3  2  1  3  4  1  -1 -1 -1 -1 -1

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Here s the complete clean and optimised code in JAVA 8 import java io    import java util     public class Solution    public static void main String   args           Take input from user       Scanner sc   new Scanner System in        int n  0      n   sc nextInt             int arr     new int n                          mean code starts here                       int sum   0      for int i 0 i lt n  i                   arr i    sc nextInt             sum    arr i              System out println  double sum n                      mean code ends here                                       median code starts here                       Arrays sort arr       int val   arr length 2      System out println  arr val  arr val-1   2 0                      median code ends here                                       mode code starts here                       int maxValue 0      int maxCount 0       for int i 0  i lt n    i                int count 0           for int j 0  j lt n    j                        if arr j     arr i                                   count                             if count  gt  maxCount                                maxCount   count                  maxValue   arr i                                      System out println maxValue                    mode code ends here

User · Answer

Yes  there does seem to be 3rd libraries  none in Java Math   Two that have come up are   http   opsresearch com app   http   www iro umontreal ca  simardr ssj indexe html  but  it is actually not that difficult to write your own methods to calculate mean  median  mode and range   MEAN  public static double mean double   m        double sum   0      for  int i   0  i  lt  m length  i              sum    m i             return sum   m length      MEDIAN     the array double   m MUST BE SORTED public static double median double   m        int middle   m length 2      if  m length 2    1            return m middle         else           return  m middle-1    m middle     2 0            MODE  public static int mode int a          int maxValue  maxCount       for  int i   0  i  lt  a length    i            int count   0          for  int j   0  j  lt  a length    j                if  a j     a i     count                    if  count  gt  maxCount                maxCount   count              maxValue   a i                        return maxValue        UPDATE  As has been pointed out by Neelesh Salpe  the above does not cater for multi-modal collections  We can fix this quite easily   public static List lt Integer gt  mode final int   numbers        final List lt Integer gt  modes   new ArrayList lt Integer gt         final Map lt Integer  Integer gt  countMap   new HashMap lt Integer  Integer gt          int max   -1       for  final int n   numbers            int count   0           if  countMap containsKey n                 count   countMap get n    1            else               count   1                     countMap put n  count            if  count  gt  max                max   count                       for  final Map Entry lt Integer  Integer gt  tuple   countMap entrySet              if  tuple getValue      max                modes add tuple getKey                          return modes        ADDITION  If you are using Java 8 or higher  you can also determine the modes like this   public static List lt Integer gt  getModes final List lt Integer gt  numbers        final Map lt Integer  Long gt  countFrequencies   numbers stream                collect Collectors groupingBy Function identity    Collectors counting           final long maxFrequency   countFrequencies values   stream                mapToLong count - gt  count               max   orElse -1        return countFrequencies entrySet   stream                filter tuple - gt  tuple getValue      maxFrequency               map Map Entry  getKey               collect Collectors toList

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Check out commons math from apache  There is quite a lot there

User · Answer

If you only care about unimodal distributions  consider sth  like this    public static Optional lt Integer gt  mode Stream lt Integer gt  stream        Map lt Integer  Long gt  frequencies   stream          collect Collectors groupingBy Function identity    Collectors counting           return frequencies entrySet   stream            max Comparator comparingLong Map Entry  getValue            map Map Entry  getKey

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As already pointed out by Nico Huysamen  finding multiple mode in Java 1 8 can be done alternatively as below   import java util ArrayList  import java util List  import java util HashMap  import java util Map   public static void mode List lt Integer gt  numArr        Map lt Integer  Integer gt  freq   new HashMap lt Integer  Integer gt          Map lt Integer  List lt Integer gt  gt  mode   new HashMap lt Integer  List lt Integer gt  gt          int modeFreq   1    record the highest frequence     for int x 0  x lt numArr size    x        1st for loop to record mode         Integer curr   numArr get x     O 1          freq merge curr  1   a  b  - gt  a   b     increment the frequency for existing element  O 1          int currFreq   freq get curr     get frequency for current element  O 1             lazy instantiate a list if no existing list  then           record mapping of frequency to element  frequency  element   overall O 1          mode computeIfAbsent currFreq  k - gt  new ArrayList lt  gt     add curr            if modeFreq  lt  currFreq  modeFreq   currFreq    update highest frequency           mode get modeFreq  forEach x - gt  System out println  Mode       x      pretty print the result   another for loop to return result     Happy coding

User · Answer

public static Set lt Double gt  getMode double   data                if  data length    0                    return new TreeSet lt  gt                               TreeMap lt Double  Integer gt  map   new TreeMap lt  gt       Map Keys are array values and Map Values are how many times each key appears in the array             for  int index   0  index    data length    index                    double value   data index                   if   map containsKey value                         map put value  1     first time  put one                                   else                       map put value  map get value    1     seen it again increment count                                             Set lt Double gt  modes   new TreeSet lt  gt       result set of modes  min to max sorted             int maxCount   1              Iterator lt Integer gt  modeApperance   map values   iterator                while  modeApperance hasNext                      maxCount   Math max maxCount  modeApperance next       go through all the value counts                           for  double key   map keySet                      if  map get key     maxCount      if this key s value is max                     modes add key     get it                                             return modes                       std dev function for good measure         public static double getStandardDeviation double   data                final double mean   getMean data               double sum   0              for  int index   0  index    data length    index                    sum    Math pow Math abs mean - data index    2                             return Math sqrt sum   data length                       public static double getMean double   data            if  data length    0                return 0                    double sum   0 0          for  int index   0  index    data length    index                sum    data index                     return sum   data length           by creating a copy array and sorting it  this function can take any data      public static double getMedian double   data            double   copy   Arrays copyOf data  data length           Arrays sort copy           return  copy length   2    0    copy copy length   2     copy copy length   2    copy  copy length   2  - 1     2

[java] How to calculate mean, median, mode and range from a set of numbers

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