Problem description & analysis:
In an Excel worksheet, a cell contains a string made up of an ordered integer sequence. There are missing numbers, and the sequence is not continuous:

1,2,3,4,5,6,7,8,9,13,14,15,16,17,18,25,26,27,28,29,30,31,32

We want to find all continuous sub-sequences, write them in the form of intervals using the hyphen, and separate intervals with the comma.

1–9,13–18,25–32

Solution:
Use SPL XLL to do this:

=spl("=?.split@pc().group@i(~!=~[-1]+1).(if(~.len()==1,~1,~1 / $[-] / ~.m(-1))).concat@c()",A1)

As shown in the picture below:

Explanation:
split@pc splits a string into a sequence, during which the function automatically parses the data type and uses a comma as the separator. group@i creates a new group whenever the specified condition is met; ~[-1] represents the directly previous members of the current one, and m(-1) is the last member of a sequence.