split_facets.R

library(egg)
library(gridExtra)
library(ggplot2)
library(grid)

d <- data.frame(x=runif(10*7),
                y=runif(10*7),
                f1 = gl(7,10), 
                f2 = gl(3, 30, 7*10))

p <- ggplot(d, aes(x,y))+
  facet_grid(f2~f1)+
  geom_line()

ld <- split(d, d$f2)
lp <- lapply(ld, `%+%`, e1 = p)
ggarrange(plots=lp)

lg <- lapply(lp, egg::set_panel_size, 
             width=unit(4,'cm'), height=unit(1,'null'))
rows <- lapply(lg, function(x) 
  arrangeGrob(rectGrob(gp=gpar(col=NA)), x, nrow=1, 
              widths = unit.c(unit(1,'null'), sum(x$widths))))
grid.newpage()
grid.arrange(grobs = rows, ncol=1)