Ajustar el tipo de línea de una línea en un facet_grid
Tengo una trama similar a esta:
b <- data.frame(x=c(1,2,3,1,2,3,1,2,3,1,2,3),y=c(1,2,3,1.5,1.9,2.5,3,2,1,2.9,1.8,1.5),c=c("1","1","1","2","2","2","1","1","1","2","2","2"),f=c("b","b","b","b","b","b","a","a","a","a","a","a"))
ggplot(b,aes(x=x,y=y,color=c,group=c))+geom_line()+facet_grid(f ~ .)
Ahora quiero que solo la línea "1" en la faceta superior "a" sea más gruesa y discontinua. es posible?