blocks|key|3078753|text|Apache+Commons+Math，特别是DescriptiveStatistics和SummaryStatistics。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3078754|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/math/|1|http://commons.apache.org/proper/commons-math/javadocs/api-3.2/org/apache/commons/math3/stat/descriptive/DescriptiveStatistics.html|2|http://commons.apache.org/proper/commons-math/javadocs/api-3.2/org/apache/commons/math3/stat/descriptive/SummaryStatistics.html^0|0|J|0|N|L|1|19|H|2|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]|$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|-4|5|6|7|Z|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]|N|$5|G|H|I|C|$J|O]]]]

<a href="http://commons.apache.org/math/" rel="noreferrer">Apache Commons Math</a>, specifically <a href="http://commons.apache.org/proper/commons-math/javadocs/api-3.2/org/apache/commons/math3/stat/descriptive/DescriptiveStatistics.html" rel="noreferrer">DescriptiveStatistics</a> and <a href="http://commons.apache.org/proper/commons-math/javadocs/api-3.2/org/apache/commons/math3/stat/descriptive/SummaryStatistics.html" rel="noreferrer">SummaryStatistics</a>.

blocks|key|323321|text|只是对这部分问题的回答：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|323322|323323|我很惊讶在java.lang.Math包中似乎没有一个函数来计算平均值……|blockquote|323324|323325|323326|我想我发现这个并不感到惊讶。有许多Java类库没有实现的“有用的算法”。他们不会实现所有的东西。在这一点上，它们与其他编程语言没有什么不同。|323327|实际上，如果Sun确实试图在J2SE中实现太多，那将是一件坏事：|323328|323329|它将花费更多的设计人员/开发人员/技术文档人员时间...如果没有明确的"return+on+investment".|ordered-list-item|323330|It“，就会增加Java的占用空间；例如，"rt.jar”的大小。对于数学空间中的事情，你通常需要以不同的方式(使用不同的API)来实现算法为了迎合不同的requirements.|323331|For复杂的事情，对于|323332|来说，最好不要尝试“标准化”API，而是把它留给其他感兴趣的/有技能的群体去做；例如，|323333|。|323334|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|10|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|11|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|13|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|14|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|15|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|17|8|@]|9|@]|A|$]]|$1|P|3|Q|5|O|7|18|8|@]|9|@]|A|$]]|$1|R|3|S|5|O|7|19|8|@]|9|@]|A|$]]|$1|T|3|U|5|O|7|1A|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|1B|8|@]|9|@]|A|$]]|$1|X|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|Y|$]]

Just responding to this part of the question:

<blockquote>
 I was quite surprised that there does
 not appear to be a function to
 calculate the Mean in the
 java.lang.Math package...
</blockquote>

I don't think I was surprised to find this. There are a lot of "useful algorithms" that the Java class libraries do not implement. They do not implement everything. And in this, they are no different from other programming languages.

Actually It would be a bad thing if Sun did try to implement too much in J2SE:

<ol>
<li>It would take more designer / developer / technical documenter time ... with no clear "return on investment".</li>
<li>It would increase the Java footprint; e.g. the size of "rt.jar". (Or if they tried to mitigate that, it would result in more platform complexity ... )</li>
<li>For things in the mathematical space, you often need to implement the algorithms in different ways (with different APIs) to cater for different requirements.</li>
<li>For complex things, it may be better for Sun not to try to "standardise" the APIs, but leave it to some other interested / skilled group to do it; e.g. the Apache folks.</li>
</ol>

blocks|key|325130|text|我认为java中没有直接的方法和类。我们必须为我们自己建造它。对于您的需求，此代码将对您有所帮助。Calculate+Standard+Deviation+in+java|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|325131|entityMap|0|LINK|mutability|MUTABLE|url|http://nscraps.com/Java/720-java-calculate-standard-deviation.htm^0|1D|10|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

I think there is no direct method and classes in java. We have to build it for our own. For your requirement this code will help you. <a href="http://nscraps.com/Java/720-java-calculate-standard-deviation.htm" rel="nofollow">Calculate Standard Deviation in java</a>

blocks|key|3292200|text|import+java.util.*;
public+class+stdevClass+{
++++public+static+void+main(String[]+args){
++++++++int+[]+list+=+{1,-2,4,-4,9,-6,16,-8,25,-10};
++++++++double+stdev_Result+=+stdev(list);
++++++++System.out.println(stdev(list));
++++}

++++public+static+double+stdev(int[]+list){
++++++++double+sum+=+0.0;
++++++++double+mean+=+0.0;
++++++++double+num=0.0;
++++++++double+numi+=+0.0;
++++++++double+deno+=+0.0;

++++++++for+(int+i+:+list)+{
++++++++++++sum%2B=i;
++++++++}
++++++++mean+=+sum/list.length;

++++++++for+(int+i+:+list)+{
++++++++++++numi+=+Math.pow((double)+i+-+mean),+2);
++++++++++++num%2B=numi;
++++++++}

++++++++return+Math.sqrt(num/list.length);
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3292201|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>import java.util.*;
public class stdevClass {
 public static void main(String[] args){
 int [] list = {1,-2,4,-4,9,-6,16,-8,25,-10};
 double stdev_Result = stdev(list);
 System.out.println(stdev(list));
 }

 public static double stdev(int[] list){
 double sum = 0.0;
 double mean = 0.0;
 double num=0.0;
 double numi = 0.0;
 double deno = 0.0;

 for (int i : list) {
 sum+=i;
 }
 mean = sum/list.length;

 for (int i : list) {
 numi = Math.pow((double) i - mean), 2);
 num+=numi;
 }

 return Math.sqrt(num/list.length);
 }
}
</code></pre>

blocks|key|325135|text|从Java+SE+8开始，平台中添加了许多类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325136|325137|java.util.DoubleSummaryStatistics|unordered-list-item|offset|length|325138|java.util.IntSummaryStatistics|325139|java.util.LongSummaryStatistics|325140|325141|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.oracle.com/javase/8/docs/api/java/util/DoubleSummaryStatistics.html|1|http://docs.oracle.com/javase/8/docs/api/java/util/IntSummaryStatistics.html|2|http://docs.oracle.com/javase/8/docs/api/java/util/LongSummaryStatistics.html^0|0|0|0|X|0|0|0|U|1|0|0|V|2|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|10|8|@]|9|@$F|11|G|12|1|13]]|A|$]]|$1|H|3|I|5|E|7|14|8|@]|9|@$F|15|G|16|1|17]]|A|$]]|$1|J|3|K|5|E|7|18|8|@]|9|@$F|19|G|1A|1|1B]]|A|$]]|$1|L|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]|U|$5|P|Q|R|A|$S|V]]|W|$5|P|Q|R|A|$S|X]]]]

Since Java SE 8 a number of classes has been added to the platform:

<ul>
<li><a href="http://docs.oracle.com/javase/8/docs/api/java/util/DoubleSummaryStatistics.html" rel="noreferrer">java.util.DoubleSummaryStatistics</a></li>
<li><a href="http://docs.oracle.com/javase/8/docs/api/java/util/IntSummaryStatistics.html" rel="noreferrer">java.util.IntSummaryStatistics</a></li>
<li><a href="http://docs.oracle.com/javase/8/docs/api/java/util/LongSummaryStatistics.html" rel="noreferrer">java.util.LongSummaryStatistics</a></li>
</ul>

Could you please suggest any simple Java statistics packages?

I don't necessarily need any of the advanced stuff. I was quite surprised that there does not appear to be a function to calculate the Mean in the <code>java.lang.Math</code> package...

What are you guys using for this?

<hr>

EDIT

Regarding:

<blockquote>
 How hard is it to write a simple class
 that calculates means and standard
 deviations?
</blockquote>

Well, not hard. I only asked this question after having hand-coded these. But it only added to my Java frustration not to have these simplest functions available at hand when I needed them. I don't remember the formula for calculating stdev by heart :)

Simple statistics - Java packages for calculating mean, standard deviation, etc

Java

你能推荐一些简单的Java统计软件包吗？我不一定需要任何高级的东西。令我相当惊讶的是，在java.lang.Math包中似乎没有一个函数来计算平均值……你们用的是什么？编辑关于：编写一个计算均值和标准差的简单类有多难？嗯，并不难。我只是在手工编写了这些代码后才问这个问题。但是，当我需要这些最简单的函数时，却不能在手边使...

问简单统计-用于计算平均值、标准差等的Java包
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