Unfortunately the ListSorter has a long-standing issue where it's not possible to sort on multiple keys, sometimes not even by chaining them one after another (see https://knowledge.safe.com/content/idea/72018/listsorter-to-support-multiple-sort-by-criteria.html)

My recommendation would be to implement any custom sorting or ordering mechanism in Python. The alternative, which perhaps is easier but is often much slower, is to explode the lists, sort the list items using the regular Sorter and then re-build the lists at the end.

Where is the list being created in the first place? Perhaps there is the option to try and address it there instead?

@bhornung

As the sorting seem not based on any "natural" type I would simply check every list for its phases.

I would add 1 element or more for the missing phase(s).

Add a attribute (SortKey) or map it.

Sortkey = (R=0, Y=1,etc) which are the desired indices and create listattribute{Sortkey} and then listsort on that.

Basically you are telling which attribute is supposed to go to which (list)index.

You could also consider to not make the schema list_index-specific (?)

You could post some sample data

I am essentially using a sort key for the list sorter, but because there is no list for R=0 , the list sorter will put y=1 as list{0}. I'm now looking into a way that I can add a blank list entry, assign it a r=0, then sort the list so that list{0} is blank except the sortkey value.

Essentially what I am trying to do is take a set of transformer records that have a 'transformerbank' id field and aggregate them so that I have one record (bank level) that contains a list of the 1-3 transformers that exist on the bank. That list must be ordered correctly so that it can be predictably inserted in the correct place in the XML template.

Essentially what I am trying to do is take a set of transformer records that have a 'transformerbank' id field and aggregate them so that I have one record (bank level) that contains a list of the 1-3 transformers that exist on the bank. That list must be ordered correctly so that it can be predictably inserted in the correct place in the XML template.

I guess my challenge is that I need a blank list entry on list{0} if there is no transformer on phase = R. I'm not sure how to add that blank list entry (placeholder).

Without a close look at the data it's hard to say what the best way to do this is, I'm presuming you're talking about having to shift all the list attributes, so everything has to shift together. I'd probably try rebuilding the list in python.

So zip all the list items together, then recreate the list in the correct order filling in the blanks. Could get messy depending on the numbers of list attributes you are working with

Quick example attached

add_to_list.fmw

Although @egomm 's python method would have worked, I had a large collection of attributes that i would have had to hard code and maintain for years to come.

I think you're looking for values/elements that has common and generate them into a list. Maybe listcombiner is suitable to perform this. Reference from https://hub.safe.com/publishers/pacific-spatial-solutions/transformers/listcombiner