Hi,
First of all, I think the reason for having cells with missing values after splitting collections is that your collections do not have the same length so when you split collections, the number of columns in your table will be the same as the number of instances in the longest collection so when the shorter collections are splitted, the remaining columns are filled with missing value.
Now how to solve your problem:
If you have deselected “Quote always” option in the configuration window of the “Column Combiner” node then your output would be like this:
a,b,c,?,?
a,b,c,d,?
a,b,?,?,?
And so on…
To remove the additional part with missing signs from the strings, you can use a “String Manipulation” node applying this expression:
regexReplace($combined string$, ",\\?.*", "")
This will modify the examples like this:
a,b,c
a,b,c,d
a,b
Best,
Armin
P.S. Follow the link @s.roughley has shared and check the solution provided by @mlauber71. There is a workflow in which the method is demonstrated.