title: Using the melt function
body: <p>I'm trying to reshape my datatable in R.  </p>
  
  <p>I've tried using the melt function, but I can't seem to get it into the format I need.</p>
  
  <p>This is my input:</p>
  
  <pre><code>structure(list(Name = c("Fred", "Peter"), first.sale = c("3/01/2019", 
  "10/08/2018"), first.result = c(352L, 209L), second.sale = c("5/12/2018", 
  "20/06/2018"), second.result = c(953L, 987L), third.sale = c("2/10/2018", 
  "21/02/2018"), third.result = c(965L, 618L), fourth.sale = c("29/08/2018", 
  "16/07/2018"), fourth.result = c(125L, 902L), fifth.sale = c("26/04/2018", 
  "5/07/2018"), fifth.result = c(264L, 71L)), .Names = c("Name", 
  "first.sale", "first.result", "second.sale", "second.result", 
  "third.sale", "third.result", "fourth.sale", "fourth.result", 
  "fifth.sale", "fifth.result"), row.names = c(NA, -2L), class = c("data.table", 
  "data.frame"))
  </code></pre>
  
  <p>and this is how i'd like my output</p>
  
  <pre><code>structure(list(Name = c("Fred", "Fred", "Fred", "Fred", "Fred", 
  "Peter", "Peter", "Peter", "Peter", "Peter", "Frank", "Frank"
  ), Sale = c("first.sale", "second.sale", "third.sale", "fourth.sale", 
  "fifth.sale", "first.sale", "second.sale", "third.sale", "fourth.sale", 
  "fifth.sale", "first.sale", "second.sale"), Result = c(352L, 
  953L, 965L, 125L, 264L, 209L, 987L, 618L, 902L, 71L, 848L, 410L
  ), SaleDate = c("3/01/2019", "5/12/2018", "2/10/2018", "29/08/2018", 
  "26/04/2018", "10/08/2018", "20/06/2018", "21/02/2018", "16/07/2018", 
  "5/07/2018", "10/08/2018", "5/12/2018")), .Names = c("Name", 
  "Sale", "Result", "SaleDate"), class = "data.frame", row.names = c(NA, 
  -12L))
  </code></pre>
  
  <p>But this is what I get when I try and use melt</p>
  
  <pre><code>structure(list(Name = c("Fred", "Peter", "Fred", "Peter", "Fred", 
  "Peter", "Fred", "Peter", "Fred", "Peter"), first.sale = c("3/01/2019", 
  "10/08/2018", "3/01/2019", "10/08/2018", "3/01/2019", "10/08/2018", 
  "3/01/2019", "10/08/2018", "3/01/2019", "10/08/2018"), second.sale = c("5/12/2018", 
  "20/06/2018", "5/12/2018", "20/06/2018", "5/12/2018", "20/06/2018", 
  "5/12/2018", "20/06/2018", "5/12/2018", "20/06/2018"), third.sale = c("2/10/2018", 
  "21/02/2018", "2/10/2018", "21/02/2018", "2/10/2018", "21/02/2018", 
  "2/10/2018", "21/02/2018", "2/10/2018", "21/02/2018"), fourth.sale = c("29/08/2018", 
  "16/07/2018", "29/08/2018", "16/07/2018", "29/08/2018", "16/07/2018", 
  "29/08/2018", "16/07/2018", "29/08/2018", "16/07/2018"), fifth.sale = c("26/04/2018", 
  "5/07/2018", "26/04/2018", "5/07/2018", "26/04/2018", "5/07/2018", 
  "26/04/2018", "5/07/2018", "26/04/2018", "5/07/2018"), variable = structure(c(1L, 
  1L, 2L, 2L, 3L, 3L, 4L, 4L, 5L, 5L), class = "factor", .Label = c("first.result", 
  "second.result", "third.result", "fourth.result", "fifth.result"
  )), value = c(352L, 209L, 953L, 987L, 965L, 618L, 125L, 902L, 
  264L, 71L)), .Names = c("Name", "first.sale", "second.sale", 
  "third.sale", "fourth.sale", "fifth.sale", "variable", "value"
  ), row.names = c(NA, -10L), class = c("data.table", "data.frame"
  ))
  </code></pre>
  
  <p>If anyone can please point me in the right direction, I'd be forever grateful.</p>
  
  <p>I think my issue is that I have two values for my variables, but can't work out how to group them.</p>