title: Sum values by same date and hour from table in R Studio
body: <p>I have a table showing date, hour, minutes, seconds, rainfall.mm</p>
  
  <p>Now I want to sum all the rainfall.mm within the same date and hour.</p>
  
  <p>The table looks like this:</p>
  
  <pre><code>      Date        Hour Minutes Seconds Rainfall.mm.
        25/05/2009   12      43      34          0.2
        26/05/2009   12      20      48          0.2
        26/05/2009   12      29      44          0.2
        26/05/2009   12      46      27          0.2
        26/05/2009   13       2      41          0.2
        26/05/2009   13      15      27          0.2
        26/05/2009   13      25      48          0.2
        26/05/2009   14      46      25          0.2
        26/05/2009   14      59       0          0.2
        26/05/2009   15       8      50          0.2
  </code></pre>
  
  <p>What I would like to end up with is a table in where the rainfall is summed by the same date and same hour like this:</p>
  
  <pre><code>      Date        Hour Minutes Seconds Rainfall.mm.
        25/05/2009   12      43      34          0.2
        26/05/2009   12      20      48          0.6
        26/05/2009   13       2      41          0.6
        26/05/2009   14      46      25          0.4
        26/05/2009   15       8      50          0.2
  </code></pre>
  
  <p>It does not really matter what the Minutes and Seconds look like.</p>
  
  <p>I have no idea how to do this, I tried several things but I am still new in R Studio and can't figure this out.</p>