reduce space between grid.arrange plots

Question

I asked a question HERE about grid arrange and got a terrific response. I want to reduce the space between plots now but get an error. First I present the code that works and then the error code (what I tried). I can't actually find grid.arrange and have always assumed it comes from gridExtra but I may be incorrect.

so 2 parts:

1. How can I reduce space between plots with grid arrange
2. Where can I find documentation about grid.arrange (Baptiste I know you maintain gridExtra so please correct my thinking or use of the package if I'm not using it in the way it was intended.)

Good code bad space

require(ggplot2);require(gridExtra)
A <- ggplot(CO2, aes(x=Plant)) + geom_bar() +
    coord_flip() + ylab("")
B <- ggplot(CO2, aes(x=Type)) + geom_bar() +coord_flip() 


 gA <- ggplot_gtable(ggplot_build(A))
 gB <- ggplot_gtable(ggplot_build(B))
 maxWidth = grid::unit.pmax(gA$widths[2:3], gB$widths[2:3])
 gA$widths[2:3] <- as.list(maxWidth)
 gB$widths[2:3] <- as.list(maxWidth)
 grid.arrange(gA, gB, ncol=1)

Bad code (my try)

require(ggplot2);require(gridExtra)
A <- ggplot(CO2, aes(x=Plant)) + geom_bar() +
    coord_flip() + ylab("") + theme(plot.margin= unit(1, "cm"))
B <- ggplot(CO2, aes(x=Type)) + geom_bar() +coord_flip() 


 gA <- ggplot_gtable(ggplot_build(A))
 gB <- ggplot_gtable(ggplot_build(B))
 maxWidth = grid::unit.pmax(gA$widths[2:3], gB$widths[2:3])
 gA$widths[2:3] <- as.list(maxWidth)
 gB$widths[2:3] <- as.list(maxWidth)
 grid.arrange(gA, gB, ncol=1)

The error:

Error in `[.unit`(theme$plot.margin, 2) : 
  Index out of bounds (unit subsetting)

Answer 1

I was misunderstanding ggplot:

require(ggplot2);require(gridExtra)
A <- ggplot(CO2, aes(x=Plant)) + geom_bar() +
    coord_flip() + ylab("") + theme(plot.margin= unit(c(1, 1, -1, 1), "lines"))
B <- ggplot(CO2, aes(x=Type)) + geom_bar() +coord_flip() + 
    theme(plot.margin= unit(rep(.5, 4), "lines"))


 gA <- ggplot_gtable(ggplot_build(A))
 gB <- ggplot_gtable(ggplot_build(B))
 maxWidth = grid::unit.pmax(gA$widths[2:3], gB$widths[2:3])
 gA$widths[2:3] <- as.list(maxWidth)
 gB$widths[2:3] <- as.list(maxWidth)
 grid.arrange(gA, gB, ncol=1)