Are these the only function supported in Glide Tables: LOG, ABS, MIN, MAX, FLOOR, CEILING, ROUND, TRUNC, ASIN, COS, ACOS, ATAN, MOD, SECOND, MINUTE, HOUR, DAY, WEEKDAY, MONTH, YEAR
Use the Get Part of URL column to extract the host. That will give you www.sofa.com.
You can then use a template to prepend the https:// if necessary.
You could also use the Extract Matching Text column with an appropriate regular expression, but personally I wouldn’t bother with that in this case.
That’s what’s supported in the Math column, but there are a whole plethora of other computed column types that allow you to do almost anything that you can dream up