Merge<https://www.jsoftware.com/help/phrases/merge_amend.htm> is a Jem<https://code.jsoftware.com/wiki/User:Dan_Bron> :
((4#'a'),(3#'b'), 2#'c') ({~ /:@/:) 0 1 2 0 1 0 2 1 0
abcabacba
Unmerge, otoh, is trivial:
'abcabacba' /: 0 1 2 0 1 0 2 1 0
aaaabbbcc
or
'abcabacba' </.~ 0 1 2 0 1 0 2 1 0
+----+---+--+
|aaaa|bbb|cc|
+----+---+--+
R.E. Boss
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