Thread: Find matching values in unequal lists and replace

I am trying to create a dynamo script that can update information (primarily cost) in furniture families. While I sort of have a working concept for how to get the existing furniture data and how to write revised data back to the families I am stumped at how to match the data between lists using the furniture id number. The lists won't be the same length, even if they are sorted by the furniture id number, and I don't know how to pair up the data dynamically because of that.

What I think I need is some way to communicate an if condition of "if a value from 'list import id' is equal to a value from 'list existing id' use the the cost data corresponding to the import id from 'list import' and replace the cost data in 'list existing' that corresponds to the existing id"

A visual draft of what I'm thinking. So far I can only figure out how to get it to work if the id's match directly.

I rebuilt your data with simple lists, but lacing and an IF statement should get you what you want.

And the graph

commitActionIf.dyn

Or one big codeblock

Thanks! It looks like it is getting a lot closer. I have two questions:

1. How do you change the lacing of a node? I see where it indicates it on the node, but can't figure out how to change them back and forth
2. How do I get it to cycle through, so that in the final result index 1 has the value 60.2 in sublist index 4 and index 2 has the value 40.11 in sublist index 4?

The lacing should do it. You right click on the node and toggle to longest.

Thanks, found the lacing.
I think there will need to be a nested if statement sort code (if that's doable in dynamo) to say
if a==b, replace value
if a/=b, cycle through list until a==b
if no pairs in the list equal each other, use the original value

Otherwise the code looks and and sees a/=b and uses the original value, instead of looking for the where the same value might be in the list.

Ah! Thank you JMK! I have been wondering what the syntax for List.GetItemAtIndex(List<LSublist>,Index) is in design script for a while. I have been using List.Map and GetItemAtIndex nodes everywhere to do the same thing :P

The reason I find this important is because when doing anything with families in revit I think it is a good idea to first get all the useful data, then make a list of lists where each sublist includes the family instance itself and the relevant data. That way nothing can go wrong with lists of unequal length or sorting, the correct data is always located with the family it comes from. But that requires always sorting and filtering by sublist data..