Occurrence in an excel serie

JosWoolley 

As someone that has moved 100% to the new Excel, I can still see some sense in what you say.  I tend to look at Excel as two computing environments that share a common function library.  I am eager to dispense with everything that characterises the legacy spreadsheet because I never liked it anyway.  The question of interest is then one of whether the new methods have matured sufficiently to offer a complete replacement for tried-and-tested wisdom of the ages.

My first approach was to use SCAN as a simple accumulator

= LET(
    offset,       DROP(VSTACK(-1,data),-1),
    start?,       data<>offset,
    end?,         DROP(VSTACK(start?, TRUE),1),
    accumulation, SCAN(0, start?, LAMBDA(a,b, IF(b=TRUE, 1, a+1))),
    frequencies,  FILTER(accumulation, end?),
    frequencies
  )

The next exploits the FREQUENCY function, though not in exactly the same manner as you.

= LET(
    index,  SEQUENCE(15),
    offset, DROP(VSTACK(data,-1),1),
    end?,   data<>offset,
    bins,   FILTER(index, end?),
    freq,   FREQUENCY(index, bins),
    DROP(freq, -1)
  )

I will have to consider your use of  ξ, η, ζ  as variable names, especially since ξ1, η1, ζ1 are valid names that haven't been squandered to support the ludicrous A1 direct referencing notation!