title: Uniting several rows of data frame
body: <p>Is there a way to unite several rows of a data frame with multiple columns?</p>
  <p>I have data from different animal organs - I want to contrast individuals' organs.
  One row should contain only measurements of an individual but from all sampled organs (columns).
  Any idea? I tried the melt command did not manage it.</p>
  <p>Here is some of my data:</p>
  <pre><code>structure(list(ID = c(&quot;BB1&quot;, &quot;BB1&quot;, &quot;BB1&quot;), ID.organ = c(&quot;BB1-B&quot;, 
  &quot;BB1-L&quot;, &quot;BB1-M&quot;), d15NAIR = c(6.244803447, 5.263374719, 6.28820367
  ), brain = c(-31.00047084, NA, NA), eyes = c(NA_real_, NA_real_, 
  NA_real_), liver = c(NA, -30.8483728, NA), muscle = c(NA, NA, 
  -29.67755736)), row.names = c(NA, 3L), class = &quot;data.frame&quot;)
  </code></pre>