Adding R^2 on graph with facets

Question

I am plotting geom_points on multiple facets and would like to annotate R^2 on each facet (preferably on the facet_label rather on the graph.) I have found some code here wh

Answer 1

The following seems to work

  lm_eqn = function(df){
    m = lm(ln_x ~ ln_y, data=df)
    eq <- substitute(~~R^2~"="~r2, 
                      list(r2 = format(summary(m)$r.squared, digits = 3)))
    c(eq = as.character(as.expression(eq)));                 
 }

Create new data frame containing R^2 for each roi_size

labeldata <- ddply(df,.(roi_size),lm_eqn )

and geom_text becomes

geom_text(data=labeldata,aes(x=1.5,y=2.2,label=eq,family="serif"), color='blue',  parse=TRUE)