I tried out using the Column Aggregator but could not get it to turn “e, b, d, c, a” into a sorted list [a, b, c, d, e], which is odd as it feels like it should be capable. Not sure what I was doing wrong.
I also took a look at the following post, which on the face of it is the same problem, and may contain the answer
but in the end, I thought I’d also just have a go. (You can never have too many variations and ideas!! :-))
This workflow also produces the result.in a somewhat convoluted way…
Broadly the task is
(1) Turn both Strings into sets of data A and B that can be compared
(2) Find where an element of set A is not in set B
(3) Mark string A as “is subset” where all of its elements are in set B
My initial stab at this had a question mark. What was the desired outcome if an element in String A is repeated. Can that occur? I had to assume that “c,c,d,e” was NOT considered a subset of “c,d,e” , and that meant I had to add some more nodes to do counts of elements and handle that bit too. So my result wasn’t as small a workflow as I’d like, but it’s another option … 
KNIME_test_is_subset.knwf (51.2 KB)