Rough method for drawing labels in intersections of a venn diagram drawn using R's `venneueler` package

venn_intersection_text.R

#install.packages('venneuler')
library(venneuler)

venn_intersection_text = function(venn, classes, label, adjustment=0.5, xadj=0, yadj=0 ){
  # fits a line between the centers of two classes and draws label text at the midpoint of that line + adjustment
  xv = adjustment*venn$centers[classes[1],1] + (1-adjustment)*venn$centers[classes[2],1] + xadj
  yv = adjustment*venn$centers[classes[1],2] + (1-adjustment)*venn$centers[classes[2],2] + yadj
  text(x=xv, y=yv, labels=label)
}

##########
## Demo ##
##########

if(FALSE){
  library(MASS)
  library(igraph)
  venn_classes = c("A", "B","A&B")
  venn_weights = c(10,50,5)
  v = venneuler(venn_classes, venn_weights, labels=as.character(venn_weights) )
  
  #par(mfrow=c(2,3))
  #m <- rbind(1:3, c(4,5,5))
  #layout(m)
  #layout.show(4)
  
  par(mfrow=c(2,1))
  
  v$labels = as.character(venn_weights[1:2])
  plot(v)
  venn_intersection_text(v, c("A","B"), venn_weights[3], 0.7)
  
  g = graph.data.frame(data.frame(src=1, tgt=2), directed=FALSE)
  V(g)$name = venn_weights[1:2]
  V(g)$size = venn_weights[1:2]*2.5
  E(g)$label = 5
  plot(g, layout = matrix(c(40,0,0,0),2))

  
  m <- rbind(c(1,2), c(3,3))
  layout(m)
    
  v$labels[1] = ""
  plot(v) 
  venn_intersection_text(v, c("A","B"), fractions(venn_weights[3]/venn_weights[2]), 0.7)
  venn_intersection_text(v, c("A","B"), "←", 0.7, yadj=-.04)
  
  v$labels = as.character(venn_weights[1:2])
  v$labels[2] = ""
  plot(v) 
  venn_intersection_text(v, c("A","B"), fractions(venn_weights[3]/venn_weights[1]), 0.7)
  venn_intersection_text(v, c("A","B"), "→", 0.7, yadj=-.04)
  
  readline(prompt="Press [enter] to continue")
  
  g = graph.data.frame(matrix(c(1,2, 2,1), 2), directed=TRUE)
  V(g)$name = venn_weights[1:2]
  V(g)$size = venn_weights[1:2]*2.5
  E(g)$label = as.character(fractions(c(venn_weights[3]/venn_weights[2], venn_weights[3]/venn_weights[1])))
  plot(g, edge.curved=TRUE, layout = matrix(c(40,0,0,0),2))
  
  par(mfrow=c(1,1))
  
}