geom_bar() + pictograms, how to?

Question

(See bottom of post for updates)

Initial post, 2014-07-29 11:43:38Z

I saw this graphics on the Economist's website and wondered if it's possible to produce a geom_bar() with this kinda illustrative icons imbedded? (dummy data below)

Dummy data,

require(ggplot2)

# Generate data
df3 <- data.frame(units = c(1.3, 1.8, 2.7, 4.2, 4.7, 6.7, 20), 
                   what = c('Wikipedia', 'London Olympic Park', 'Aircraft carrier', 
                            'The Great Pyramid', 'Stonehenge', 'Burj Khalifas', 
                            'Empire State Building'))

# make gs an ordered factor
df3$what <- factor(df3$what, levels = df3$what, ordered = TRUE)

    #plots
    ggplot(df3, aes(what, units)) + geom_bar(fill="white", colour="darkgreen", 
           alpha=0.5, stat="identity") + coord_flip() + scale_x_discrete() + 
           scale_y_continuous(breaks=seq(0, 20, 2)) + theme_bw() + 
           theme(axis.title.x  = element_blank(), axis.title.y  = element_blank())

Update #1, 2014-07-29 15:07:51Z

Apparently Robert Grant has started to build an R function to produce bar-charts with pictograms, it can be found at Github. Thanks to Andrie for that information. I'm currently working to see if Robert's function can do what I am looking for.

Please chime in if you have any advice on how to answer my question using Robert's function.

Update #2, 2014-08-02 12:35:19Z

Here is a simple illustration of how Grant's R-pictogram-function work

# in case you don't alredy have RCurl
# install.packages("RCurl", dependencies = TRUE)
source_github <- function(u) {
  # load package
  require(RCurl)

  # read script lines from website and evaluate
  script <- getURL(u, ssl.verifypeer = FALSE)
  eval(parse(text = script),envir=.GlobalEnv)
}

Got this script form this SO answer

source_github("https://raw.githubusercontent.com/robertgrant/pictogram/master/pictogram.R")

# install.packages("png", dependencies = TRUE)
  require(png)

img <- readPNG(system.file("img", "Rlogo.png", package="png"))
pictogram(icon = img, n = c( 12, 35, 7),
grouplabels=c("12 R logos","35 R logos","7 R logos"))

This gives you this kinda plot

Answer 1

Here's what I have come up with based on this idea. R logo taken from Wikipedia.

library(png)
fill_images <- function()
{
  l <- list()
  for (i in 1:nrow(df3)) 
  {
    for (j in 1:floor(df3$units[i]))
    {
      #seems redundant, but does not work if moved outside of the loop (why?)
      img <- readPNG("~/../Rlogo.png")
      g <- rasterGrob(img, interpolate=TRUE)
      l <- c(l, annotation_custom(g, xmin = i-1/2, xmax = i+1/2, ymin = j-1, ymax = j))
    }
  }
  l
}

p <- ggplot(df3, aes(what, units)) + 
  geom_bar(fill="white", colour="darkgreen", alpha=0.5, stat="identity") + 
  coord_flip() + 
  scale_y_continuous(breaks=seq(0, 20, 2)) + 
  scale_x_discrete() + 
  theme_bw() + 
  theme(axis.title.x  = element_blank(), axis.title.y  = element_blank()) + 
  fill_images()
p

I'm not quite sure what's the best way to draw partial images though.

Update:

Actually, that was easier than I had expected. I clip the image by drawing a white rectangle over a part of it. Note that geom_bar should be on top so that the clipping rectangle won't affect it. There was a minor issue with grid lines (they were partly hidden by these white rectangles), so I had to hardcode the position of these and restore them manually. Not an ideal solution, of course, but I don't know how to programmatically retrieve the grid position. Anyway, the final plot does the job and it also looks fancy!

library(png)
fill_images <- function()
{
  l <- list()
  for (i in 1:nrow(df3)) 
  {
    for (j in 1:ceiling(df3$units[i]))
    {
      img <- readPNG("~/../Rlogo.png")
      g <- rasterGrob(img, interpolate=TRUE)
      l <- c(l, annotation_custom(g, xmin = i-1/2, xmax = i+1/2, ymin = j-1, ymax = j))
    }
  }
  l
}

clip_images <- function(restore_grid = TRUE)
{
  l <- list()
  for (i in 1:nrow(df3)) 
  {
    l <- c(l, geom_rect(xmin = i-1/2, xmax = i+1/2, 
                        ymin = df3$units[i], ymax = ceiling(df3$units[i]),
                        colour = "white", fill = "white"))
    if (restore_grid && ceiling(df3$units[i]) %in% major_grid) 
      l <- c(l, geom_segment(x = i-1, xend = i+1,
                             y = ceiling(df3$units[i]), 
                             yend = ceiling(df3$units[i]),
                             colour = grid_col, size = grid_size))
  }
  l
}

grid_col <- "grey50"
grid_size <- 0.6
major_grid <- 0:10 * 2
p <- ggplot(df3, aes(what, units)) + 
  fill_images() + 
  clip_images() +
  geom_bar(fill=NA, colour="darkgreen", size=1.2, alpha=0.5, stat="identity") + 
  coord_flip() + 
  scale_y_continuous(breaks=seq(0, 20, 2)) + 
  scale_x_discrete() + 
  theme_bw() + 
  theme(axis.title.x  = element_blank(), axis.title.y  = element_blank(),
        panel.grid.major.x = element_line(colour = grid_col, size = grid_size), 
        panel.grid.major.y = element_line(colour = NA)) 
p

In order to save the .svg file, use e.g.

ggsave(file="test.svg", plot=p, width=10, height=8)

If you want to have a filling image as an .svg file, take a look at grImport package. It seems you'll have to convert .svg to .ps manually (e.g. with imagemagick), and then follow the guide.