title: R: aggregate by ID and find min Date and Time
body: <p>I’m a R beginner and having difficulty with the following pretty simple problem;
  I have the following transaction data:</p>
  
  <pre><code>Data
  Row#ID     Lable    Date          Time
  4   15275   John    2000-05-16    16:15:00
  7   15275   John    2000-05-16    16:25:00
  22  15276   Bob     2000-07-04    18:05:00
  25  15276   Bob     2000-08-07    05:23:00
  10  1234    Kate    2000-06-17    18:07:00
  13  1234    Kate    2000-06-21    06:49:00 
  </code></pre>
  
  <p>And need to generate a unique entry for each ID with the minimum Date and minimum Time, 
  Similar to this:</p>
  
  <pre><code>Row#    ID          Lable   Date        Time
          15275   John        2000-05-16  16:15:00
          15276   Bob         2000-07-04  18:05:00
          1234    Kate        2000-06-17  18:07:00
  </code></pre>
  
  <p>I have tried </p>
  
  <pre><code>unique&lt;-aggregate(Date$Date ,list(Data$ID, Data$Time,unique_Data$Lable ), min)
  </code></pre>
  
  <p>to no avail. </p>
  
  <p>Any assistance would be greatly appreciated. 
  Thanks</p>