title: Duplication when merging bulk nodes with attributes
body: <p>I can't see from documentation how to merge bulk data with attributes. The example here uses R but the solution will be Cypher.  I need to designate <code>id</code> as the unique field so that the node will not be duplicated when attributes are changed or new attribute data is added.</p>
  
  <pre><code>x = data.frame(id = 1:2, name = c('Kate','Charles'), 
                 age = c(27,34), grp = c('A','B'), stringsAsFactors = F)
  
  merge_df_with_graph = function(x, graph, query){
    t = newTransaction(graph)
    for (i in 1:nrow(x)) {
      appendCypher(t, query, id = x$id[i], name = x$name[i], 
                   age = x$age[i], grp = x$grp[i])
    }
    commit(t)
  }
  
  merge_df_with_graph(x, graph, "MERGE (n:User {id:{id}, name:{name}});")
  n = getNodes(graph, 'MATCH (n) RETURN (n);')
  length(n)
  #&gt; [1] 2
  
  # when an attribute changes
  x$name[2] = 'Charlie'
  merge_df_with_graph(x, graph, "MERGE (n:User {id:{id}, name:{name}});")
  n = getNodes(graph, 'MATCH (n) RETURN (n);')
  length(n)
  #&gt; [1] 3
  
  # when new attributes data is added
  merge_df_with_graph(x, graph, "MERGE (n:User {id:{id}, name:{name}, age:{age}});")
  n = getNodes(graph, 'MATCH (n) RETURN (n);')
  length(n)
  #&gt; [1] 5
  </code></pre>
  
  <p>I'm new to neo4j and the <a href="http://neo4j.com/docs/developer-manual/current/cypher/clauses/create-unique/" rel="nofollow noreferrer">example in documentation</a> doesn't specify how to define attributes other than the unique key.  Grateful for assistance.</p>