title: Find repeated data from index and string it together
body: <p>Using R, if I have a 2 column data frame:</p>
  
  <pre><code>meta &lt;- c(1,2,2,3,4,4,4,5)
  value &lt;- c("a","b","c","d","e","f","g","h")
  df &lt;- data.frame(meta,value)
  df
    meta value
  1    1     a
  2    2     b
  3    2     c
  4    3     d
  5    4     e
  6    4     f
  7    4     g
  8    5     h
  </code></pre>
  
  <p>How would I go about combining "value" with a delimiter (like ||) by repeated "meta" such that the resulting data frame would look like:</p>
  
  <pre><code>  meta   value
  1    1       a
  2    2    b||c
  3    3       d
  4    4 e||f||g
  5    5       h
  </code></pre>
  
  <p>Thanks!</p>