ggplot2: Using gtable to move strip labels to top of panel for facet_grid

This takes your first approach. It inserts a row above each of the panels, grabs the strip grobs (on the right), and inserts them into the new rows.

library(ggplot2)library(gtable)library(grid)mt <- ggplot(mpg, aes(x = cty, y = model)) + geom_point() +  facet_grid(manufacturer ~ ., scales = 'free', space = 'free') +  theme(panel.spacing = unit(0.5, 'lines'),          strip.text.y = element_text(angle = 0))# Get the gtablegt <- ggplotGrob(mt)# Get the position of the panels in the layoutpanels <-c(subset(gt$layout, grepl("panel", gt$layout$name), se=t:r))# Add a row above each panelfor(i in rev(panels$t-1)) gt = gtable_add_rows(gt, unit(.5, "lines"), i)# Get the positions of the panels and the strips in the revised layoutpanels <-c(subset(gt$layout, grepl("panel", gt$layout$name), se=t:r))strips <- c(subset(gt$layout, grepl("strip-r", gt$layout$name), se=t:r))# Get the strip grobsstripText = gtable_filter(gt, "strip-r")# Insert the strip grobs into the new rowsfor(i in 1:length(strips$t)) gt = gtable_add_grob(gt, stripText$grobs[[i]]$grobs[[1]],  t=panels$t[i]-1, l=4)# Remove the old stripsgt = gt[,-5]# For this plot - adjust the heights of the strips and the empty row above the stripsfor(i in panels$t) {   gt$heights[i-1] = unit(0.8, "lines")   gt$heights[i-2] = unit(0.2, "lines")   }# Draw itgrid.newpage()grid.draw(gt)

OR, you can achieve the second approach using a facet_wrap_labeller function available from here.

library(ggplot2)library(gtable)mt <- ggplot(mpg, aes(x = cty, y = model)) + geom_point() +   facet_wrap(~ manufacturer, scales = "free_y", ncol = 1) +   theme(panel.margin = unit(0.2, 'lines'))facet_wrap_labeller <- function(gg.plot, labels=NULL) {  require(gridExtra)  g <- ggplotGrob(gg.plot)  gg <- g$grobs        strips <- grep("strip_t", names(gg))  for(ii in seq_along(labels))  {    modgrob <- getGrob(gg[[strips[ii]]], "strip.text",                        grep=TRUE, global=TRUE)    gg[[strips[ii]]]$children[[modgrob$name]] <- editGrob(modgrob,label=labels[ii])  }  g$grobs <- gg  class(g) = c("arrange", "ggplot",class(g))   return(g)}## Number of y breaks in each panelg <- ggplot_build(mt) N <- sapply(lapply(g$panel$ranges, "[[", "y.major"), length)# Some arbitrary strip textsStripTexts = expression(gamma[1], sqrt(gamma[2]), C, `A really incredibly very very very long label`, gamma[5], alpha[1], alpha[2], `Land Rover`, alpha[1], beta[2], gamma^2, delta^2, epsilon[2], zeta[3], eta[4] ) # Apply the facet_wrap_labeller functiongt = facet_wrap_labeller(mt, StripTexts)# Get the position of the panels in the layoutpanels <- gt$layout$t[grepl("panel", gt$layout$name)]# Replace the default panel heights with relative heightsgt$heights[panels] <- lapply(N, unit, "null")# Draw itgt

I was struggling with a similar problem but putting the labels on the bottom. I've used a code adaptation of this answer. And recently found that

ggplot2 ver.2.2.1.0 (http://docs.ggplot2.org/current/facet_grid.html)

~facet_grid(.~variable,switch='x')

option which has worked beautifully for me.