Bug: GroupBy Node Append Elements not working as expected

I have a list column and as aggregation I’m choosing “Append Elements” with “Filter missing collection elements” unchecked.


However the generated output list never contains any missing collection elements. Either I don’t understand the option correctly (Filter missing collection elements) or it isn’t working. In fact the option doesn’t have any effect on the output. This applies to KNIME 3.7.2 and KNIME 4 and possibly earlier versions.

See attached workflow for an example.

Append Elements.knwf (8.2 KB)

The wording should be filter out missing…
If you realy would like to get only thw missing values use the row filter node…

I want all the collection elements regardless if they are missing or not. See example.

Hi there,

I have checked it and seems like a bug. Will check it and get back to you.

Tnx for reporting this.



Hi there,

Just as an alternative approach, I suggest using Ungroup node before the GroupBy node and then use the List method in the GroupBy node. That will solve your issue for now.


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Sadly this doesn’t work in my case because I have multiple sub-groups, meaning several columns containing to the same “sub-group” with same amount of elements in the list. One subgroup could have 2 elements and another 10. This leads to additional rows which then when grouping again leads to additional, wrong missing values. So I need to split the table up in these subgroups and then do the ungroup -> group and join again. Safe to say a fix for this issue would help me a lot.

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