plot DAG using DiagrammeR

DAG.R

library(DiagrammeR)
library(DiagrammeRsvg)
library(rsvg)

g1 <- grViz("digraph{
                     node[shape = plaintext]
                     U[label = 'U', shape=circle]
                     X[label = 'X']
                     Z[label = 'Z']
                     Y[label = 'Y']
           { rank=same; X; Z; Y; }
                     U -> X
                     X -> Z
                     Z -> Y
                     U -> Y
                     }")

print(g1)
rsvg_png(charToRaw(export_svg(g1)), 
         "graph1.png",
         width = 500, height = 500)

g2 <- grViz("digraph{
                     node[shape = plaintext]
                     U[label = 'U', shape=circle]
                     X[label = 'X']
                     Z[label = 'Z']
                     Y[label = 'Y']
           { rank=same; X; Z; Y; }
                     U -> X
                     Z -> X 
                     X -> Y
                     U -> Y
                     }")

print(g2)
rsvg_png(charToRaw(export_svg(g2)), 
         "graph2.png",
         width = 500, height = 500)