Juxtapose tableGrob with ggplot2 y-axis - r

Question

Is there an elegant way to align the tableGrob rows with the axis breaks?
I would like to juxtapose a tableGrob and ggplot chart in R (I need to reproduce some SAS output used in previous versions of a public report). Like this minimal reproducible example:
This post got me pretty far --- the tableGrob is in the same gtable row as the body of the chart; however, it requires lots of manual fiddling to get the rows in the tableGrob to line up with the axis labels.
I also found this post. Since I'm Sweaving a public report, I would prefer not to use code that isn't readily available in a package on CRAN. That being said, the experimental version of tableGrob appears to accept heights as an argument. If this code will do the trick, and I do choose to use this experimental version, how would I calculate the appropriate row heights?
If there is not an elegant way of doing this, I found these tricks to be helpful:
set fontsize AND cex in tableGrob to match ggplot2
set padding.v to space table rows in tableGrob
modify coordinate limits to accomodate column labels and align with bottom of last row
My MRE code:
library(ggplot2)
library(gridExtra)
library(gtable)
theme_set(theme_bw(base_size = 8))
df <- head(mtcars,10)
df$cars <- row.names(df)
df$cars <- factor(df$cars, levels=df$cars[order(df$disp, decreasing=TRUE)], ordered=TRUE)
p <- ggplot(data=df, aes(x=hp, y=cars)) +
geom_point(aes(x=hp, y=cars)) +
scale_y_discrete(limits=levels(df$cars))+
theme(axis.title.y = element_blank()) +
coord_cartesian(ylim=c(0.5,length(df$cars)+1.5))
t <- tableGrob(df[,c("mpg","cyl","disp","cars")],
cols=c("mpg","cyl","disp","cars"),
gpar.coretext = gpar(fontsize = 8, lineheight = 1, cex = 0.8),
gpar.coltext = gpar(fontsize = 8, lineheight = 1, cex = 0.8),
show.rownames = FALSE,
show.colnames = TRUE,
equal.height = TRUE,
padding.v = unit(1.65, "mm"))
g <- NULL
g <- ggplotGrob(p)
g <- gtable_add_cols(g, unit(2,"in"), 0)
g <- gtable_add_grob(g, t, t=3, b=3, l=1, r=1)
png('./a.png', width = 5, height = 2, units = "in", res = 100)
grid.draw(g)
dev.off()
I have left the car names on the y-axis breaks for troubleshooting purposes, but ultimately I will remove them.

Answer 1

There's now this experimental version of gtable_table
table <- gtable_table(df[,c("mpg","cyl","disp","cars")],
heights = unit(rep(1,nrow(df)), "null"))
g <- ggplotGrob(p)
g <- gtable_add_cols(g, sum(table$widths), 0)
g <- gtable_add_grob(g, table, t=3, b=3, l=1, r=1)
grid.newpage()
grid.draw(g)

Answer 2

#Baptiste's answer expanded to demonstrate column labels and cell parameters:
library(ggplot2)
library(gridExtra)
## I manually changed the dependency on
install.packages(".//gtable_0.2.tar.gz", repos = NULL, type="source")
## The forked version of gtable requires R version 3.2.0
## which is currently in development (as of 9/17/2014) due to change in grid
## (https://github.com/wch/r-source/commit/850a82c30e91feb47a0b6385adcbd82988d90413)
## I have not installed the development version.
## However, I was able, in limited testing, to get this to work with R 3.1.0
## and ggplot2_1.0.0
## YRMV
## The following code, commented out, may be more useful with release of R 3.2.0
## library(devtools)
## devtools::install_github("baptiste/gtable")
library(gtable)
theme_set(theme_bw(base_size = 10))
df <- mtcars
df$cars <- row.names(df)
df <- head(df[,c("mpg","cyl","disp","cars")],10)
df$cars <- factor(df$cars, levels=df$cars[order(df$disp, decreasing=TRUE)], ordered=TRUE)
p <- ggplot(data=df, aes(x=disp, y=cars)) +
geom_point(aes(x=disp, y=cars)) +
scale_y_discrete(limits=levels(df$cars))+
theme(axis.title.y = element_blank()) +
coord_cartesian(ylim = c(0.5,nrow(df)+1))
core <- gtable_table(df[order(df$disp, decreasing=FALSE),],
fg.par = list(fontsize=c(8)),
bg.par = list(fill=c(rep("lightblue",4),rep("white",4)), alpha=0.5),
heights = unit(rep(1,nrow(df)), "null"))
colHead <- gtable_table(t(colnames(df)),
fg.par = list(fontsize=c(8)),
bg.par = list(fill=c(1), alpha=0.2),
heights = unit(0.5, "null"))
table1 <- rbind(colHead, core)
g <- ggplotGrob(p)
g <- gtable_add_cols(g, sum(table1$widths), 0)
g <- gtable_add_grob(g, table1, t=3, b=3, l=1, r=1)
grid.newpage()
grid.draw(g)