This is best demonstrated by example:
Input:
1 2 2 1 1 1 2 3 3
Output:
1; 2 2; 1 1 1; 2; 3 3
┌─┬───┬─────┬─┬───┐
│1│2 2 │1 1 1│2│3 3│
└─┴───┴─────┴─┴───┘
So I'm looking for something like Key /., but Key would group all ones together, all twos together, and so on. I want to group only contiguous runs together.
One final thought: Key can be used successfully, if I can first generate an x for it that looks like this:
0 1 1 2 2 2 3 4 4 NB. x suitable for use in Key
1 2 2 1 1 1 2 3 3 NB. original data
I cannot think of a tacit solution for generating such an x, though (my ideas involve a mutating temporary variable to store the current "label", ie, the numbers 0 through 4 in the x defined above)