How to calculate mean, median, mode and range from a set of numbers
Yes, there does seem to be 3rd libraries (none in Java Math). Two that have come up are:
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 SORTEDpublic 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;}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;}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());}
public static Set<Double> getMode(double[] data) { if (data.length == 0) { return new TreeSet<>(); } TreeMap<Double, Integer> map = new TreeMap<>(); //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<Double> modes = new TreeSet<>(); //result set of modes, min to max sorted int maxCount = 1; Iterator<Integer> 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; }