如何从一组数字计算平均值，中位数，模式和范围

本文介绍了如何从一组数字计算平均值，中位数，模式和范围的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

是否有任何函数（作为数学库的一部分）将计算意味着，中位数，模式和范围来自一组数字。

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

推荐答案

是的，似乎确实有第3个库（Java Math中没有）。其中两个是：

Yes, there does seem to be 3rd libraries (none in Java Math). Two that have come up are:

http：// opsresearch。 com / app /

www.iro.umontreal.ca/~simardr/ssj/indexe.html

但实际上并非如此难以编写自己的方法来计算平均值，中位数，模式和范围。

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; } }

模式

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

正如Neelesh Salpe所指出的，上述内容并不适合多模式收藏。我们可以很容易地解决这个问题：

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

如果您使用的是Java 8或更高版本，您还可以确定以下模式：

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()); }