The converse to split is the join function, which takes a list of strings and joins them together again.I don't understand what meaning of converse you use here. English is not my first language - but here is what I found for 'converse' in the Meriam-Webster online dictionary:
No. The converse to a split is a regular expression (with matching). The idea here is that with matching you specify what you want to match and you get that as a return value ala @simpsons = "Bart Lisa Maggie Marge Homer" =~ /(\w+)/g). With split you specify all the things you don't want and you get everything else. Which one you use depends on what is more natural to specify.
something reversed in order, relation, or action: as a : a theorem formed by interchanging the hypothesis and conclusion of a given theorem b : a proposition obtained by interchange of the subject and predicate of a given proposition <"no P is S " is the converse of "no S is P ">I believe the OP used 'converse' as a synonim for 'inverse' in the mathematical sense, i.e. he wanted to say that split o join = identity. Which is quite close to being correct.
Or perhaps you meant join in the first sentence? This possibillity occured to me just after posting this comment.