Find longest string with criteria

The core of this formula is the MATCH function, which locates the position of the longest string using supplied criteria:

MATCH(MAX(LEN(names)*(class=F5)),LEN(names)*(class=F5),0)

Note MATCH is set up to perform an exact match by supplying zero for match type. For lookup value, we have:

LEN(names)*(class=F5)

The LEN function returns an array of results (lengths), one for each name in the list where class = "A" from cell F5 :

{5;6;8;6;6;0;0;0;0;0}

This effectively filters out all of Class B, and the MAX function then returns the largest value, 8.

To construct a lookup array, we use the same approach:

LEN(names)*(class=F5)

And get the same result:

{5;6;8;6;6;0;0;0;0;0}

After LEN and MAX run, we have a MATCH formula with these values:

MATCH(8,{5;6;8;6;6;0;0;0;0;0},0))

MATCH then returns the position of 8 in the list, 3, which feeds into INDEX like this:

=INDEX(names,3)

Finally, INDEX dutifully returns the value in the 3rd position of names, which is "Jonathan".