Sort Array ASC Label Members as BEG, MID and END

Greetings.  I prefer to be able to do this utilizing M instead of DAX.  I have a table that will have two columns: one is the ID (Text) and the other, MD, contains integers.  I want to sort the table and then calculate a new column called POSITION to identify the first member of each unique ID array as BEG, the last as END, and all others as MID.  Example:

ID     MD    POSITION

A       1       BEG

A       2       MID

A       3       MID

A       4       END

B       3       BEG

B       7       MID         

B     12       MID

B     30       END

.....

Thanks.