Adjusting the "margin" space for axis text in ggplot2

Question

Which property, if any, in ggplot controls
the width (or amount of blank space) of the axis text?

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In the example below, my ultimate goal is to "push in" the left-hand side of the top graph so that it lines up with the bottom graph.

I tried theme(plot.margin=..) but that affects the margin of the entire plot.
facet'ing doesn't help either, since the scales on the y are different.

As a last resort, I realize I could modify the axis text itself, but then I would also need to calculate the cuts for each graph.

Reproducible Example:

library(ggplot2)
library(scales)

D <- data.frame(x=LETTERS[1:5],  y1=1:5, y2=1:5 * 10^6)

P.base <- ggplot(data=D, aes(x=x)) + 
            scale_y_continuous(labels=comma)

Plots <- list(
    short = P.base + geom_bar(aes(y=y1), stat="identity", width=.5)
  , long  = P.base + geom_bar(aes(y=y2), stat="identity", width=.5) 
  )

do.call(grid.arrange, c(Plots, ncol=1, main="Sample Plots"))

Answer 1

Here is one solution.

The idea was borrowed from "Having horizontal instead of vertical labels on 2x1 facets and splitting y-label Define a function

align_plots1 <- function (...) {
    pl <- list(...)
    stopifnot(do.call(all, lapply(pl, inherits, "gg")))
    gl <- lapply(pl, ggplotGrob)
    bind2 <- function(x, y) gtable:::rbind_gtable(x, y, "first")
    combined <- Reduce(bind2, gl[-1], gl[[1]])
    wl <- lapply(gl, "[[", "widths")
    combined$widths <- do.call(grid::unit.pmax, wl)
    grid::grid.newpage()
    grid::grid.draw(combined)
}

short <- P.base + geom_bar(aes(y=y1), stat="identity", width=.5)
long <- P.base + geom_bar(aes(y=y2), stat="identity", width=.5) 

#Now, align the plots
align_plots1(short, long)

Here is the output.