Problem description & analysis:

In the Excel table below, both column A and column B contain semicolon-separated strings:

Task: Find the difference between column A and column B, which consists of items that are contained in column A but not contained in column B, and separate the result with the semicolon:

Solution:

Use SPL XLL to get this done:

=spl("=?.((~1.split($[;]) \ ~2.split($[;])).concat($[;]))",A1:B3)

As shown in the picture below:

Explanation:

~1 represents the first child member of the current member (row); \ is the operator for computing the difference; $[] represents a string.