How to Transpose if duplicates

After much trial and error and searching for a solution, I'm stumped. I'm not even sure you need a macro for this but maybe. I have a worksheet of over 20,000 rows of data. I've sorted the data by column B. I need to combine and transpose (starting at column C) when there are like-duplicates. The example below should explain it clearly. It doesn't matter whether the output is separated by commas or separated into cells.


A1 B1 C1 (Desired Output)

A A A A, A C, A P, A M, A E, A F, A G
C A
P A
M A
E A
F A
G A
H B B H, B A, B R, B K, B L, B N, B O
A B
R B
K B
L B
N B
O B
U C C U, C H
H C
Y D D Y, D E, D P
E D
P D

etc...

Thanks for the help.

It took out spaces between letters in the example, so to make it easier to understand I attached an excel spreadsheet.

Wow, that's a really impressive formula. I'm going to have to spend some more time with it to fully understand it. I think it's close but I can't seem to modify it to make it work the way I need it to. I attached a much clearer example, using names.

Since I couldn't seem to find a solution anywhere for this, I hope that your effort is useful to more users than just me. Thanks again.