R help - Mar 2010 - Keeping only one date for each patient ID and disease SITE

Dear List Subscribers,

   I am working on the following problem and was wondering if
there is some command or set of commands to solve it:
  Thank you in advance,
  Eric

1.       The dataset Cancer0 may have multiple dates of treatment (DATE) for
each patient (ID) with a given disease (SITE).  Create a new dataset by keeping
only the record with earliest treatment date for each patient and disease site.
 
Dataset: Cancer0
 
OBS    ID       SEX    AGE    DODX         SITE          DATE               DOSE
FRAC
 
1       1001       M       60   09NOV1986    LUNG      03JAN1987          5000  
20
2       1001       M       60   09NOV1986    LUNG      03JAN1987          5000  
20
3       1002       F        58    07JUN1993    BREAST   03FEB1994           4000
16
4       1002       F        58    07JUN1993    BREAST  05MAR1994           1000 
5
5       1003       M       63   11OCT1990     LUNG     15DEC1990            3000
25
6       1003       M       63   11OCT1990     LUNG      18FEB1991            800
5
7       1003       M       59  24MAR1986      SKIN     23AUG1987             200
1
8       1004       F        48   30JUL1995    LARYNX  22SEP1995           3500  
25
 

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