4.1 Multiple Plots per Page

In order to succeed plotting several of our previously created plots on one page, there’s two things of importance:

1. The lattice and ggplot2 plot objects need to be printed using print , and
2. We need to set newpage = FALSE in the print call so that the previously drawn elements are not deleted.

Let’s try and plot some of these plots next to each other on one page by setting up a suitable viewport structure. First of all, we obviously need to produce plots. Note that we will use very basic plots here, but this should work with whatever lattice or ggplot2 object you have created earlier.

p1_lattice <- xyplot(price ~ carat, data = diamonds)
p2_lattice <- histogram(~ price, data = diamonds)

p1_ggplot <- ggplot(aes(x = carat, y = price), data = diamonds) +
  geom_point()
p2_ggplot <- ggplot(diamonds, aes(x = price)) +
  geom_histogram()

### clear plot area
grid.newpage()

### define first plotting region (viewport)
vp1 <- viewport(x = 0, y = 0, 
                height = 0.5, width = 0.5,
                just = c("left", "bottom"),
                name = "lower left")

### enter vp1 
pushViewport(vp1)

### show the plotting region (viewport extent)
grid.rect()

### plot a plot - needs to be printed (and newpage set to FALSE)!!!
print(p1_lattice, newpage = FALSE)

### leave vp1 - up one level (into root vieport)
upViewport(1)

### define second plot area
vp2 <- viewport(x = 1, y = 0, 
                height = 0.5, width = 0.5,
                just = c("right", "bottom"),
                name = "lower right")

### enter vp2
pushViewport(vp2)

### show the plotting region (viewport extent)
grid.rect()

### plot another plot
print(p2_lattice, newpage = FALSE)

### leave vp2
upViewport(1)


vp3 <- viewport(x = 0, y = 1, 
                height = 0.5, width = 0.5,
                just = c("left", "top"),
                name = "upper left")

pushViewport(vp3)

### show the plotting region (viewport extent)
grid.rect()

print(p1_ggplot, newpage = FALSE)

upViewport(1)


vp4 <- viewport(x = 1, y = 1, 
                height = 0.5, width = 0.5,
                just = c("right", "top"),
                name = "upper right")

pushViewport(vp4)

### show the plotting region (viewport extent)
grid.rect()

print(p2_ggplot, newpage = FALSE)

upViewport(1)

Figure 4.5: Using grid to arrange multiple plots on one page.

So there we have it. Creating and navigating between viewports enables us to build a graphical layout in whatever way we want. In our opinion, this is way better than saving all the plots to the hard drive and then using some sort of graphics software such as Adobe Photoshop or Inkscape to arrange the plots onto one page. After all, sometimes we may have several of these multi-plot pages that we want to produce. As of now, we know how to do this automatically, thus rendering any post-production steps unnecessary.