Using Listutils in java in the java code node, it is possible to get list.size() i.e no of elements in a string array. However it does not seem to work if the list has spaces and not commas. Try using list and set in groupby for instance to get spaces and commas as separators.
I am trying to use the subset matcher node to match two lists and it returns a list for which the result of list.size() is always 1, as it contains spaces between elements. If the original list contains comma separated elements, i get the correct size. So its only a problem for groupby and subset matcher output when elements in a set are separated by space.