title: Change position of nodes in Sankey
body: <p>How can I change position of the nodes in my Sankey Diagram vertically (y axis) to look like the example below with red nodes:
  <a href="https://i.stack.imgur.com/GGWiQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GGWiQ.png" alt="enter image description here"></a></p>
  
  <p>My dataset:</p>
  
  <pre><code>&gt; dput(final_df_2)
  structure(list(individual_id = c(21L, 21L, 22L, 23L, 24L, 24L, 
  24L, 25L, 26L, 26L, 26L, 26L, 26L, 26L, 26L, 27L, 27L, 27L, 27L
  ), number = c(1L, 2L, 1L, 1L, 1L, 2L, 3L, 1L, 1L, 2L, 3L, 4L, 
  5L, 6L, 7L, 1L, 2L, 3L, 4L), treatment = structure(c(5L, 3L, 
  2L, 4L, 1L, 5L, 3L, 2L, 3L, 5L, 2L, 5L, 4L, 5L, 1L, 2L, 5L, 5L, 
  3L), .Label = c("Adalimumab", "Etanercept", "Infliximab", "Rituximab", 
  "(Missing)"), class = "factor")), row.names = c(1L, 2L, 8L, 14L, 
  20L, 26L, 27L, 33L, 39L, 45L, 46L, 52L, 53L, 59L, 60L, 66L, 72L, 
  73L, 74L), class = "data.frame")
  </code></pre>
  
  <p>My code:</p>
  
  <pre><code>install.packages("alluvial")
  library(alluvial)
  
  ggplot(final_df_2 , aes(x = number, stratum = treatment, alluvium = individual_id, fill = treatment, label = treatment)) +
    scale_fill_brewer(type = "qual", palette = "Set3") +
    geom_flow(width = 1/10) +
    geom_stratum(width = 1/10, colour = NA) +
    scale_x_continuous(breaks = 1:7, labels = c("1st Therapy", "2nd Therapy", "3rd Therapy", "4th Therapy", "5th Therapy", "6th Therapy", "7th Therapy"))+
    ggtitle("Treatment across observation period")+
    theme_minimal()+
    theme( panel.grid.major = element_blank(),
           panel.grid.minor = element_blank(), axis.text.y = element_blank())
  </code></pre>