xml_demo.R

# XML package demo.
# Create barplot of distribution of first letters
# in the Mondial database.
# RS15082015

library(XML)
library(ggplot2)

# Load data.
xml <- xmlTreeParse("~/Temp/mondial-3.0.xml", useInternalNodes = TRUE)  

# Find what we are looking for.
root <- xmlRoot(xml)
city.names <- unlist(xpathApply(root, "//country/city/name", xmlValue, trim = TRUE))

# Create temporary data frame for better handling.
counts.df <- data.frame(letter = LETTERS, 
                        count = sapply(LETTERS, function(L) {
                          length(city.names[grepl(paste("^", L, sep = ""), city.names)])
                          }))

# Now make a nice looking barplot.
p <- ggplot(counts.df, aes(x = factor(letter), y = count, 
                           fill = rep(c("1", "2"), 13))) + 
  geom_bar(stat = "identity")
p <- p + labs(title = "Empirical Distribution of First Letters", 
              x = "Letters", y = "Count", fill = NULL)
p <- p + scale_fill_brewer(palette = "Set1") + guides(fill = FALSE)
plot(p)