blocks|key|916044|text|您使用的是哪个版本的Apache+Commmons+Math？至少在2.1版本中有一个中级类(旧版本我不确定)。您可以将其用作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916045|Median+median+=+new+Median();
median.evaluate(values);|code-block|syntax|javascript|916046|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Which version of Apache Commmons Math are you using? There is a median class at least in 2.1 onwards (older version i am not sure). You can use it as:

<pre><code>Median median = new Median();
median.evaluate(values);
</code></pre>

blocks|key|1664237|text|将所有数字放入一个列表中，对该列表进行排序，然后取中间值(或两个中间值的平均值，以获得偶数大小)。不需要计算|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1664238|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Put all the numbers into a list, sort the list, and take the middle value (or the average of the two middle values for even size). No calculations necessary

blocks|key|916023|text|尝试Median对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|916024|entityMap|0|LINK|mutability|MUTABLE|url|http://commons.apache.org/math/api-2.0/org/apache/commons/math/stat/descriptive/rank/Median.html^0|2|6|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]]]]

Try the <a href="http://commons.apache.org/math/api-2.0/org/apache/commons/math/stat/descriptive/rank/Median.html" rel="nofollow noreferrer">Median</a> object.

blocks|key|916070|text|将值放入一个列表对象中。让我们假设这些值是整数，这个列表叫做"+values“。然后|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916071|List<Integer>+values;
...+populate+values+...
Collections.sort(values);
int+median;
int+midpoint=values.size()/2;
if+(values.size()%252==1)
++median=values.get(midpoint%2B1).intValue();
else
++median=(values.get(midpoint).intValue()%2Bvalues.get(midpoint%2B1).intValue())/2;|code-block|syntax|javascript|916072|如果值的数量很大，比如数百或更多，那么修改mod-2在技术上可能是正确的，但却是多余的。|916073|也许有一种更有效的方法可以做到这一点--对大型列表进行排序相当慢--但这种方法是可行的。|916074|哦，你真的应该检查一下没有条目的列表。也许我遗漏了其他边界条件。|916075|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Get the values into a List object. Let's suppose the values are integers and the list is called "values". Then

<pre><code>List&lt;Integer&gt; values;
... populate values ...
Collections.sort(values);
int median;
int midpoint=values.size()/2;
if (values.size()%2==1)
 median=values.get(midpoint+1).intValue();
else
 median=(values.get(midpoint).intValue()+values.get(midpoint+1).intValue())/2;
</code></pre>

If the number of values is large, like in the hundreds or more, messing with the mod-2 may be technically correct but superfluous.

Maybe there's a more efficient way to do it -- sorting is pretty slow on a large list -- but this would work.

Oh, and you really should check for a list with zero entries. Maybe I'm missing other boundary conditions.

blocks|key|2798137|text|来自“我手上的时间太多”部门:这是一个小的MedianGenerator类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2798138|/**
+*+Methods+to+calculate+the+median+value+of+a+supplied+{@link+List}.
+*/
public+final+class+MedianGenerator{

++++private+MedianGenerator(){
++++}

++++/**
+++++*+Calculate+the+median+of+a+supplied+list.
+++++*+<ol>
+++++*+<li>A+copy+will+be+generated</li>
+++++*+<li>this+copy+will+be+sorted+with+the+supplied+comparator</li>
+++++*+<li>the+median+will+be+calculated,+using+the+supplied+averageCalculator
+++++*+for+collections+with+an+even+number+of+items</li>
+++++*+</ol>
+++++*+
+++++*+@param+data+
+++++*+@param+comparator
+++++*+@param+averageCalculator
+++++*+@return+the+median
+++++*/
++++public+static+<T>+T+calculateMedian(final+List<T>+data,
++++++++final+Comparator<?+super+T>+comparator,
++++++++final+AverageCalculator<T>+averageCalculator){
++++++++final+List<T>+copy+=+new+ArrayList<T>(data);
++++++++Collections.sort(copy,+comparator);
++++++++return+doCalculateMedian(data,+averageCalculator);

++++}

++++/**
+++++*+Calculate+the+median+of+a+supplied+list.
+++++*+<ol>
+++++*+<li>A+copy+will+be+generated</li>
+++++*+<li>this+copy+will+be+sorted+with+the+supplied+comparator</li>
+++++*+<li>the+median+will+be+calculated,+using+the+{@link+#ALWAYS_FIRST}+{@link+AverageCalculator}
+++++*+for+collections+with+an+even+number+of+items</li>
+++++*+</ol>
+++++*+
+++++*+@param+data+
+++++*+@param+comparator
+++++*+@return+the+median
+++++*/
++++@SuppressWarnings("unchecked")
++++public+static+<T>+T+calculateMedian(final+List<T>+data,
++++++++final+Comparator<?+super+T>+comparator){
++++++++return+calculateMedian(data,+comparator,+(AverageCalculator<T>)+ALWAYS_FIRST);
++++}

++++/**
+++++*+Calculate+the+median+of+a+supplied+list.
+++++*+<ol>
+++++*+<li>A+copy+will+be+generated</li>
+++++*+<li>this+copy+will+be+sorted+using+natural+ordering</li>
+++++*+<li>the+median+will+be+calculated,+using+the+{@link+#ALWAYS_FIRST}+{@link+AverageCalculator}
+++++*+for+collections+with+an+even+number+of+items</li>
+++++*+</ol>
+++++*+
+++++*+@param+data+
+++++*+@return+the+median
+++++*/
++++@SuppressWarnings("unchecked")
++++public+static+<T+extends+Comparable<?+super+T>>+T+calculateMedian(final+List<T>+data){
++++++++return+calculateMedian(data,+(AverageCalculator<T>)+ALWAYS_FIRST);
++++}

++++/**
+++++*+Calculate+the+median+of+a+supplied+list.
+++++*+<ol>
+++++*+<li>A+copy+will+be+generated</li>
+++++*+<li>this+copy+will+be+sorted+using+natural+ordering</li>
+++++*+<li>the+median+will+be+calculated,+using+the+supplied+averageCalculator
+++++*+for+collections+with+an+even+number+of+items</li>
+++++*+</ol>
+++++*+
+++++*+@param+data
+++++*+@param+averageCalculator+
+++++*+@return+the+median
+++++*/
++++public+static+<T+extends+Comparable<?+super+T>>+T+calculateMedian(final+List<T>+data,
++++++++final+AverageCalculator<T>+averageCalculator){
++++++++final+List<T>+copy+=+new+ArrayList<T>(data);
++++++++Collections.sort(copy);
++++++++return+doCalculateMedian(copy,+averageCalculator);
++++}

++++private+static+<T>+T+doCalculateMedian(final+List<T>+sortedData,
++++++++final+AverageCalculator<T>+averageCalculator){
++++++++T+result;
++++++++if(sortedData.isEmpty()){
++++++++++++result+=+null;
++++++++}+else{
++++++++++++final+int+size+=+sortedData.size();
++++++++++++if(size+%25+2+==+0){
++++++++++++++++result+=
++++++++++++++++++++averageCalculator.getAverage(sortedData.get(size+/+2+-+1),
++++++++++++++++++++++++sortedData.get(size+/+2));
++++++++++++}+else{
++++++++++++++++result+=+sortedData.get(size+/+2+-+1);
++++++++++++}

++++++++}
++++++++return+result;
++++}

++++/**
+++++*+Generic+accessor+method+for+{@link+#ALWAYS_FIRST}.
+++++*/
++++@SuppressWarnings("unchecked")
++++public+static+<T>+AverageCalculator<T>+alwaysFirst(){
++++++++return+ALWAYS_FIRST;
++++}

++++/**
+++++*+{@link+AverageCalculator}+implementation+that+always+returns+the+lower
+++++*+bound+unchanged.
+++++*/
++++@SuppressWarnings("rawtypes")
++++public+static+final+AverageCalculator+ALWAYS_FIRST+=
++++++++new+AverageCalculator(){

++++++++++++@Override
++++++++++++public+Object+getAverage(final+Object+first,+final+Object+second){
++++++++++++++++return+first;
++++++++++++}

++++++++};

++++/**
+++++*+When+there+is+an+even+number+of+items,+this+interface+is+used+to+generate
+++++*+the+average+between+the+two+middle+items.
+++++*/
++++public+static+interface+AverageCalculator<E>+{

++++++++E+getAverage(E+first,+E+second);
++++}

}|code-block|syntax|javascript|2798139|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

From the "too-much-time-on-my-hands" department: here is a little MedianGenerator class:

<pre><code>/**
 * Methods to calculate the median value of a supplied {@link List}.
 */
public final class MedianGenerator{

 private MedianGenerator(){
 }

 /**
 * Calculate the median of a supplied list.
 * &lt;ol&gt;
 * &lt;li&gt;A copy will be generated&lt;/li&gt;
 * &lt;li&gt;this copy will be sorted with the supplied comparator&lt;/li&gt;
 * &lt;li&gt;the median will be calculated, using the supplied averageCalculator
 * for collections with an even number of items&lt;/li&gt;
 * &lt;/ol&gt;
 * 
 * @param data 
 * @param comparator
 * @param averageCalculator
 * @return the median
 */
 public static &lt;T&gt; T calculateMedian(final List&lt;T&gt; data,
 final Comparator&lt;? super T&gt; comparator,
 final AverageCalculator&lt;T&gt; averageCalculator){
 final List&lt;T&gt; copy = new ArrayList&lt;T&gt;(data);
 Collections.sort(copy, comparator);
 return doCalculateMedian(data, averageCalculator);

 }

 /**
 * Calculate the median of a supplied list.
 * &lt;ol&gt;
 * &lt;li&gt;A copy will be generated&lt;/li&gt;
 * &lt;li&gt;this copy will be sorted with the supplied comparator&lt;/li&gt;
 * &lt;li&gt;the median will be calculated, using the {@link #ALWAYS_FIRST} {@link AverageCalculator}
 * for collections with an even number of items&lt;/li&gt;
 * &lt;/ol&gt;
 * 
 * @param data 
 * @param comparator
 * @return the median
 */
 @SuppressWarnings("unchecked")
 public static &lt;T&gt; T calculateMedian(final List&lt;T&gt; data,
 final Comparator&lt;? super T&gt; comparator){
 return calculateMedian(data, comparator, (AverageCalculator&lt;T&gt;) ALWAYS_FIRST);
 }

 /**
 * Calculate the median of a supplied list.
 * &lt;ol&gt;
 * &lt;li&gt;A copy will be generated&lt;/li&gt;
 * &lt;li&gt;this copy will be sorted using natural ordering&lt;/li&gt;
 * &lt;li&gt;the median will be calculated, using the {@link #ALWAYS_FIRST} {@link AverageCalculator}
 * for collections with an even number of items&lt;/li&gt;
 * &lt;/ol&gt;
 * 
 * @param data 
 * @return the median
 */
 @SuppressWarnings("unchecked")
 public static &lt;T extends Comparable&lt;? super T&gt;&gt; T calculateMedian(final List&lt;T&gt; data){
 return calculateMedian(data, (AverageCalculator&lt;T&gt;) ALWAYS_FIRST);
 }

 /**
 * Calculate the median of a supplied list.
 * &lt;ol&gt;
 * &lt;li&gt;A copy will be generated&lt;/li&gt;
 * &lt;li&gt;this copy will be sorted using natural ordering&lt;/li&gt;
 * &lt;li&gt;the median will be calculated, using the supplied averageCalculator
 * for collections with an even number of items&lt;/li&gt;
 * &lt;/ol&gt;
 * 
 * @param data
 * @param averageCalculator 
 * @return the median
 */
 public static &lt;T extends Comparable&lt;? super T&gt;&gt; T calculateMedian(final List&lt;T&gt; data,
 final AverageCalculator&lt;T&gt; averageCalculator){
 final List&lt;T&gt; copy = new ArrayList&lt;T&gt;(data);
 Collections.sort(copy);
 return doCalculateMedian(copy, averageCalculator);
 }

 private static &lt;T&gt; T doCalculateMedian(final List&lt;T&gt; sortedData,
 final AverageCalculator&lt;T&gt; averageCalculator){
 T result;
 if(sortedData.isEmpty()){
 result = null;
 } else{
 final int size = sortedData.size();
 if(size % 2 == 0){
 result =
 averageCalculator.getAverage(sortedData.get(size / 2 - 1),
 sortedData.get(size / 2));
 } else{
 result = sortedData.get(size / 2 - 1);
 }

 }
 return result;
 }

 /**
 * Generic accessor method for {@link #ALWAYS_FIRST}.
 */
 @SuppressWarnings("unchecked")
 public static &lt;T&gt; AverageCalculator&lt;T&gt; alwaysFirst(){
 return ALWAYS_FIRST;
 }

 /**
 * {@link AverageCalculator} implementation that always returns the lower
 * bound unchanged.
 */
 @SuppressWarnings("rawtypes")
 public static final AverageCalculator ALWAYS_FIRST =
 new AverageCalculator(){

 @Override
 public Object getAverage(final Object first, final Object second){
 return first;
 }

 };

 /**
 * When there is an even number of items, this interface is used to generate
 * the average between the two middle items.
 */
 public static interface AverageCalculator&lt;E&gt; {

 E getAverage(E first, E second);
 }

}
</code></pre>

Is there any built in library that I can use for calculating median in java??

I was working with apache.commons.math for other statistical functions but median was nowhere to be found.

Thank you,

Statistical calculations

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在java中有没有内置的库可以用来计算中位数？？我正在使用apache.commons.math进行其他统计函数的工作，但找不到median。谢谢,

问统计计算
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回答 5

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