r - Different y-Axis Labels facet_grid and sizes

Question

I'am stuck with the following problem:

I want to display different characteristics of a timeseries in one plot (with multiple subplots). To align the chart areas and for easy creation I use ggplot2 and its facet_grid function.

However, I want to change just one axis label (eg. the upper plot to percent).

Furthermore, I want to resize the heights of each plot, so that the upper plot is roughly twice as large as the lower one.

Thank you very much for your help!

Example

require(ggplot2)

#simulate some data
df <- data.frame(date=c(1:1000),
              value=cumsum(rnorm(1000)),
              volume=abs(rnorm(1000)*10))

#melt for ggplot
df_melt <- melt(df, id=c("date"),measure.vars=c("value","volume"))

#plot
ggplot(df_melt, aes(x=date, y=value)) + geom_line() + 
       facet_grid(variable~., scales = "free")

which results in something like this:

Answer 1

You can change the grobs of your plot to do this

library(ggplot2)
library(grid)
library(scales)

#plot
p <- ggplot(df_melt, aes(x=date, y=value)) + 
            geom_line() + 
            facet_grid(variable~., scales = "free")

# change facet heights
g1 <- ggplotGrob(p) 
g1$heights[[3]] <- unit(2, "null") 

# change labels - create second plot with percentage labels (nonsese % here)
p2 <- ggplot(df_melt, aes(x=date, y=value)) + 
              geom_line() + 
              facet_grid(variable~., scales = "free") +
              scale_y_continuous(labels = percent_format())

g2 <- ggplotGrob(p2) 

#Tweak axis - overwrite one facet
g1[["grobs"]][[2]] <- g2[["grobs"]][[2]]

grid.newpage()
grid.draw(g1)