# Aggregation method extension

**URL:** <https://forum.knime.com/t/aggregation-method-extension/7646>\
**Category:** Node Development\
**Created:** [April 8, 2015, 5:03pm UTC](https://forum.knime.com/t/aggregation-method-extension/7646 "2015-04-08T17:03:06Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![swebb](https://forum-cdn.knime.com/user_avatar/forum.knime.com/swebb/32/369_2.png) [@swebb](https://forum.knime.com/u/swebb)\
**Post date:** [April 8, 2015, 5:03pm UTC](https://forum.knime.com/t/aggregation-method-extension/7646/1 "2015-04-08T17:03:06Z")

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Hi

I'm tying to add some new methods to the GroupBy node to work with my BitSetCell. I took a look at&nbsp;BitVectorUnionOperator and replicated the functionality to work on BitSetsCells.&nbsp;

I then added to the AggregationOperator extension point.&nbsp;

\<extension&nbsp;point="org.knime.base.AggregationOperator"\>  
&nbsp; &nbsp; \<AggregationOperator  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; AggregationOperator="org.lhasalimited.knime.bitset.util.BitSetAndOperator"  
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; deprecated="false"\>  
&nbsp; &nbsp; \</AggregationOperator\>  
&nbsp;\</extension\>

I don't see my option in the GroupBy node, is there something else I need to do?

Cheers

Sam

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**Author:** ![tobias.koetter](https://forum-cdn.knime.com/user_avatar/forum.knime.com/tobias.koetter/32/56844_2.png) [@tobias.koetter](https://forum.knime.com/u/tobias.koetter)\
**Post date:** [April 9, 2015, 12:05pm UTC](https://forum.knime.com/t/aggregation-method-extension/7646/2 "2015-04-09T12:05:00Z")

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Hi Sam,

I guess the problem is related to a missing default constructor (e.g. a public consturctor with no arguments) . If this constructor is missing your extension can not be loaded via the plugin mechanism. The constructor could look like the following:

```
/ **Default constructor.** /
public BitSetAndOperator() {
  super(new OperatorData(... your operator specific settings...));
}
```

You can also have a look at the first paragraph of the _AggregationOperator_ java doc for more details on this.

The _BitVectorUnionOperator_ does not require this constructor since it is added manually to the AggregationOperators and not loaded via the plugin mechanism (see line 255 of the _AggregationMethods_ class).

Let me know if that solved the problem.

Bye,

Tobias

&nbsp;

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**Author:** ![swebb](https://forum-cdn.knime.com/user_avatar/forum.knime.com/swebb/32/369_2.png) [@swebb](https://forum.knime.com/u/swebb)\
**Post date:** [April 9, 2015, 12:32pm UTC](https://forum.knime.com/t/aggregation-method-extension/7646/3 "2015-04-09T12:32:47Z")

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Hi Tobias

Spot on! It now shows up, I should read the Javadoc better in future.&nbsp;

Thank you

Sam

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**Author:** ![tobias.koetter](https://forum-cdn.knime.com/user_avatar/forum.knime.com/tobias.koetter/32/56844_2.png) [@tobias.koetter](https://forum.knime.com/u/tobias.koetter)\
**Post date:** [April 9, 2015, 3:04pm UTC](https://forum.knime.com/t/aggregation-method-extension/7646/4 "2015-04-09T15:04:41Z")

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Perfect. Thanks for the feedback.  
&nbsp;

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**Author:** ![system](https://forum-cdn.knime.com/uploads/default/original/1X/ab3ccf34482a0329361734a18199390177204f15.png) [@system](https://forum.knime.com/u/system)\
**Post date:** [June 23, 2023, 8:25pm UTC](https://forum.knime.com/t/aggregation-method-extension/7646/5 "2023-06-23T20:25:06Z")

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