Constant width in ggplot barplots - r

Question

How to make the width of bars and spaces between them fixed for several barplots using ggplot, having different number of bars on each plot?
Here is a failed try:
m <- data.frame(x=1:10,y=runif(10))
ggplot(m, aes(x,y)) + geom_bar(stat="identity")
ggplot(m[1:3,], aes(x,y)) + geom_bar(stat="identity")
Adding width=1 to geom_bar(...) doesn't help as well. I need the second plot automatically to have less width and the same bar width and spaces as the first one.

Answer 1

Edit:
It appears the OP simply wants this:
library(gridExtra)
grid.arrange(p1,arrangeGrob(p2,widths=c(1,2),ncol=2), ncol=1)
I am not sure, if it's possible to pass absolute widths to geom_bar. So, here is an ugly hack:
set.seed(42)
m <- data.frame(x=1:10,y=runif(10))
p1 <- ggplot(m, aes(x,y)) + geom_bar(stat="identity")
p2 <- ggplot(m[1:3,], aes(x,y)) + geom_bar(stat="identity")
g1 <- ggplotGrob(p1)
g2 <- ggplotGrob(p2)
I used str to find the correct grob and child. You could use more sophisticated methods to generalize this if necessary.
#store the old widths
old.unit <- g2$grobs[[4]]$children[[2]]$width[[1]]
#change the widths
g2$grobs[[4]]$children[[2]]$width <- rep(g1$grobs[[4]]$children[[2]]$width[[1]],
length(g2$grobs[[4]]$children[[2]]$width))
#copy the attributes (units)
attributes(g2$grobs[[4]]$children[[2]]$width) <- attributes(g1$grobs[[4]]$children[[2]]$width)
#position adjustment (why are the bars justified left???)
d <- (old.unit-g2$grobs[[4]]$children[[2]]$width[[1]])/2
attributes(d) <- attributes(g2$grobs[[4]]$children[[2]]$x)
g2$grobs[[4]]$children[[2]]$x <- g2$grobs[[4]]$children[[2]]$x+d
#plot
grid.arrange(g1,g2)

Answer 2

Wrapped the other suggestions in a function that only requires a single graph.
fixedWidth <- function(graph, width=0.1) {
g2 <- graph
#store the old widths
old.unit <- g2$grobs[[4]]$children[[2]]$width[[1]]
original.attibutes <- attributes(g2$grobs[[4]]$children[[2]]$width)
#change the widths
g2$grobs[[4]]$children[[2]]$width <- rep(width,
length(g2$grobs[[4]]$children[[2]]$width))
#copy the attributes (units)
attributes(g2$grobs[[4]]$children[[2]]$width) <- original.attibutes
#position adjustment (why are the bars justified left???)
d <- (old.unit-g2$grobs[[4]]$children[[2]]$width[[1]])/2
attributes(d) <- attributes(g2$grobs[[4]]$children[[2]]$x)
g2$grobs[[4]]$children[[2]]$x <- g2$grobs[[4]]$children[[2]]$x+d
return(g2)
}