Help with random selection and variable criteria

Hi - I have asample spreadsheet with 3 columns : ref number, Type, and User.
I want to select a random sample based on the user and type of activity.
The number of sample to be variable based each user /type - all my attempts sofar have failed miserably.
I presume I would need to loop through each User and type for each number ofrandom selections and indicate these as selected on another column
I can then move the selected items to another individual user work sheet
Would anyone be able to assist ? sample of the worksheet is attached

Many thanks in advance