Constant width in ggplot barplots

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)
}

Answer 3

I solved a similar problem with:

mywidth = .5
ggplot(m, aes(x,y)) + 
    geom_col(width=log(1 + length(unique(m$x))) * mywidth)

Because geom_bar() tries to adjust bar width based on how many unique values there are of the x-axis variable, log() "undoes" this by rapidly increasing as the number of unique values of x increases, "flattening" the cumulative geom_bar() + custom width to a constant value.

The 1 + is just to deal with log(1)=0.

You can adjust the value of mywidth as you like.