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.

Answer 1

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 < 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 < a.length; ++i) {         int count = 0;         for (int j = 0; j < a.length; ++j) {             if (a[j] == a[i]) ++count;         }         if (count > maxCount) {             maxCount = count;             maxValue = a[i];         }     }      return maxValue; } 

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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<Integer> mode(final int[] numbers) {     final List<Integer> modes = new ArrayList<Integer>();     final Map<Integer, Integer> countMap = new HashMap<Integer, Integer>();      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 > max) {             max = count;         }     }      for (final Map.Entry<Integer, Integer> tuple : countMap.entrySet()) {         if (tuple.getValue() == max) {             modes.add(tuple.getKey());         }     }      return modes; } 

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ADDITION

If you are using Java 8 or higher, you can also determine the modes like this:

public static List<Integer> getModes(final List<Integer> numbers) {     final Map<Integer, Long> countFrequencies = numbers.stream()             .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));      final long maxFrequency = countFrequencies.values().stream()             .mapToLong(count -> count)             .max().orElse(-1);      return countFrequencies.entrySet().stream()             .filter(tuple -> tuple.getValue() == maxFrequency)             .map(Map.Entry::getKey)             .collect(Collectors.toList()); }