Combining a column's data by referencing another

[jimmy coleman]

I've received warehouse inventory and need to reorganize the data into the appropriate columns. My specific issue is concerning the column named new_description

The file has :

column A with part numbers, some are the same, some are not. (ie. 1,1,1 2,2,3,4...7)
column C with a description different in every row. (ie. red, blue, green.....)

column F must have the following info:

for all part numbers that repeat I want to add (concatenate?) their description into a single cell beginning and separated by "<li>" (ie. for part number 1 there are three entries with 3 descriptions each containing a different color; in column F I'd like it to say <li>red<li>blue<li>green)

I can do it manually as I show in the attached file.... however the full list is 5000 products or more in a few separate files so a formula to help automate this is crucial.

Can anyone offer some direction or a formula to help me eliminate as much repetition as possible?