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From: "Thomas Neidhart (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (MATH-1046) math3.stat.Frequency: Allow Null
 keys (comparable objects)
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    [ https://issues.apache.org/jira/browse/MATH-1046?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13804569#comment-13804569 ] 

Thomas Neidhart commented on MATH-1046:
---------------------------------------

{quote}
I don't think this will solve the "null" issue unless you stipulate a class/interface
to handle this issue (make it an Optional<T>?) 
{quote}

No, but the interface of the addValue will change, allowing you to provide any type you specify for the Frequency object, not only Comparable. Together with a custom Comparator it should be more flexible.

btw. there is already a constructor which supports a Comparator, so we just need to update the addValue(...) methods.

> math3.stat.Frequency: Allow Null keys (comparable objects)
> ----------------------------------------------------------
>
>                 Key: MATH-1046
>                 URL: https://issues.apache.org/jira/browse/MATH-1046
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.2
>         Environment: Linux, JDK 7
>            Reporter: Hugo Ferrira
>            Priority: Trivial
>              Labels: features
>             Fix For: 3.2
>
>
> The class {{math3.stat.Frequency}} uses a {{TreeMap}} which does not allow
> for the use of null keys ({{public void addValue(Comparable<?> v)}} with {{v = null}}). I am analyzing data (matrix) whose values may 
> contain nulls. I need to get the counts for elements in a given column.
> This includes knowing how many are null. This information will be used
> for data cleaning/pre-processing.
>  A simple change would be substituting {{TreeMap}} with {{java.util.HashMap<K,V>}}. 



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