求ArrayList元素平均值的最短形式

Question

By shortest form I mean least number of lines of java codes. I would like to get average value of items of an ArrayList of integer values. For example for the ArrayList ar :

ArrayList<Integer> ar = new ArrayList<Integer>(Arrays.asList(1,2,3,5,8,13,21));

I am looking for something like

ar.Average()

or

ar.Sum()

or

Arrays.Average(ar)

PS. I know we can do it in a loop. Just looking for a shorter alternative;

Answer 1

You could use a Math library such as Apache Commons Math.

http://commons.apache.org/math/apidocs/index.html

Specifically a SummaryStaticics object ( http://commons.apache.org/math/apidocs/src-html/org/apache/commons/math3/stat/descriptive/SummaryStatistics.html#line.123 ). Though for something like average, it probably isn't worth importing a library.

Answer 2

The commons math library contains a mean as well as whatever else you probably want for simple statistics. Perhaps exactly what your looking for?

Answer 3

If you're already using Java 8:

double average = Arrays.asList(1, 2, 3, 4)
                       .stream()
                       .map(Integer::intValue)
                       .average()
                       .getAsDouble();

Answer 4

代码行始终是一种毫无意义的措施，但是如果这是您所关心的：

int sum=0;for(Integer i:ar)sum += i;System.out.println(sum);