Adding blank option while working with User input (KNIME Server)


I am building a Web application (on KNIME Server) and have the following use case.

My data(in a table) needs aggregation on several levels based on the user input. I have created a workflow with 4 column selection widgets to take 4 user inputs and pass it to a Groupby node as 4 flow variables, and these flow variables will then perform the aggregation inside the Groupby node.

I need an solution, where the user selects only 2(or less than 4) aggregation levels and leaves the other 2 user input as blank. How is it possible to add a blank option in the column selection widget? I tried to add a blank column, but the workflow doesnt get executed then.


Hello @AkshayPrakash ,

we have moved your post under Analytics Platform category since your question is more related to workflow building than KNIME Server issue. Also the Analytics Platform category has higher visibility, in this way more people could see your post giving a chance them to answer it :slight_smile:

Have you tried to find some example workflow similar to your use case on the HUB? This one seems to me similar, it uses the default value in the column selection widget when no changes is required in that selection level (not exactly the same but maybe it worth checking for inspiration). Re-execution functionality of the Column Selection Widget ā€“ KNIME Community Hub

Also if you could share a simple wf with dummy data it would be easier to us or to others here in the Forum to advise.


1 Like


the dummy data would look like this-

I have created the following workflow-


Inside the component (Select groups for aggregation)-

My current workflow supports a default value, but I need it such that the user can do the aggregation(sum of values), even if they select just 2(or less than 4) groups for aggregation and leave the other 2 blank(i.e, without a default value). I need a solution such that, out of the 4 user inputs( for which columns to aggregate), even if the user chooses to just aggregate based on 2 groups(leaving the other 2 choices blank), the aggregation in the groupby node should happen.

Thanks and regards,

Hello @AkshayPrakash ,

Iā€™m not sure if it is possible to achieve what you want with using the Column Selection Widget node. I leave the stage for others answering this:)
But here is another approach with the Multiple Selection Widget node, I hope it will help you!

Forum_groupby_flow_variable 1.knwf (20.7 KB)


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