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Adding legend to venn diagram

I am using library VennDiagram to plot venn diagrams. But this function does not have a functionality to add legend and set names are displayed on or close to the sets themselves.

library(VennDiagram)
x <- list(c(1,2,3,4,5),c(4,5,6,7,8,9,10))
venn.diagram(x,filename="test.png",fill=c("#80b1d3","#b3de69"),
             category.names=c("A","B"),height=500,width=500,res=150)

venn-diagram

And with many sets, overplotting names is an issue and I would like to have a legend instead. The function is built on grid graphics and I have no idea how grid plotting works. But, I am attempting to add a legend anyway.

Looking into the venn.diagram function, I find that final plotted object is grob.list and it is a gList object and its plotted using grid.draw(). 

png(filename = filename, height = height, width = width, 
    units = units, res = resolution)
grid.draw(grob.list)
dev.off()

I figured out that I could create a legend by modifying the venn.diagram function with the code below.

cols <- c("#80b1d3","#b3de69")
lg <- legendGrob(labels=category.names, pch=rep(19,length(category.names)),
                 gp=gpar(col=cols, fill="gray"),byrow=TRUE)

Draw the object lg

png(filename = filename, height = height, width = width, 
    units = units, res = resolution)
grid.draw(lg)
dev.off()

to get a legend

legend

How do I put the venn diagram (gList) and the legend (gTree,grob) together in a usable way? I am hoping to get something like base plot style:

plot-with-legend

or the ggplot style

plit-with-legend

Solution

  • If you want to continue using the VennDiagram package and learn a bit of grid on the way:

    Prepare diagram and legend

    library(VennDiagram)
x <- list(c(1,2,3,4,5),c(4,5,6,7,8,9,10))
diag <- venn.diagram(x,NULL,fill=c("#80b1d3","#b3de69"),
             category.names=c("A","B"),height=500,width=500,res=150)


cols <- c("#80b1d3","#b3de69")
lg <- legendGrob(labels=c("A","B"), pch=rep(19,length(c("A","B"))),
                 gp=gpar(col=cols, fill="gray"),
                 byrow=TRUE)

    Transform the diagram to a gTree

    (I'd love to find a better way if anyone knows one)

    library(gridExtra)

g <- gTree(children = gList(diag))

    Plot the two gTrees side by side

    gridExtra::grid.arrange(g, lg, ncol = 2, widths = c(4,1))

    Or one above the other

    grid.arrange(g, lg, nrow = 2, heights = c(4,1))