Get index of true value in list /match with list

hi yall
I’am new to dynamo so not used to many kinds of nodes
so in this pictue
I want to have each list of external walls -[W01, W02]and internal walls[P01,P02]
I already made a model has walls name maked as W01, W02,P01,P02 …blahblah
So in the end i want to get /sum of internal walls area/ and /sum of external walls area/

Thanks a lot

Flip the inputs, the node is asking is x equal to y. So, you want to compare your “external wall” value against the values in the list, right now it’s comparing the values in the list to your “external wall” value. See the example below.
Hope this helps!