title: Getting rowSums for triplicate records and retaining only the one with highest value
body: <p>I have a data frame with 163 observations and 65 columns with some animal data. The 163 observations are from 56 animals, and each was supposed to have triplicated records, but some information was lost so for the majority of animals, I have triplicates ("A", "B", "C") and for some I have only duplicates (which vary among "A" and "B", "A" and "C" and "B" and "C"). </p>
  
  <p>Columns 13:65 contain some information I would like to sum, and only retain the one triplicate with the higher rowSums value. So my data frame would be something like this:</p>
  
  <pre><code>  ID    Trip     Acet    Cell   Fibe   Mega   Tera
  1   4      A        2       4      9      8      3  
  2   4      B        9       3      7      5      5  
  3   4      C        1       2      4      8      6 
  4   12     A        4       6      7      2      3 
  5   12     B        6       8      1      1      2 
  6   12     C        5       5      7      3      3 
  
  </code></pre>
  
  <p>I am not sure if what I need is to write my own function, or a loop, or what the best alternative actually is - sorry I am still learning and unfortunately for me, I don't think like a programmer so that makes things even more challenging...</p>
  
  <p>So what I want is to know to keep on rows 2 and 6 (which have the highest rowSums among triplicates per animal), but for the whole data frame. What I want as a result is</p>
  
  <pre><code>    ID    Trip    Acet    Cell   Fibe   Mega   Tera
  1   4      B       9       3      7      5      5  
  2   12     C       5       5      7      3      3
  
  </code></pre>
  
  <p>REALLY sorry if the question is poorly elaborated or if it doesn't make sense, this is my first time asking a question here and I have only recently started learning R.</p>