library(RCurl)
library(reshape)
library(htmltab)
library(ggplot2)
library(stringr)
library(scales)

#get the table from the url
theurl <- getURL("https://en.wikipedia.org/wiki/Nationwide_opinion_polling_for_the_United_States_presidential_election,_2016", ssl.verifyPeer=FALSE)
table <- htmltab(theurl, which=3)

df = table[, c(2, 8, 3:6)]

names(df) <- c("Date", "Size", "DC", "DP", "RC", "RP")

df = df[which(df$RC=="Donald Trump"), ]
df[which(df$DC=="Bernie Sanders"), ]$DC = "Sanders"
df[which(df$DC=="Hillary Clinton"), ]$DC = "Clinton"
df[which(df$RC=="Donald Trump"), ]$RC = "Trump"
df[which(df$DC=="Sanders" & df$RC=="Trump"), ]$RC = "Trump2"

df$Contest = paste(substr(df$DC, 1, 1), substr(df$RC, 1, 1))

dem.df = df[, c(1:4, 7)]
rep.df = df[, c(1:2, 5:7)]

names(dem.df)[3:4] <- c("Candidate", "Support")
names(rep.df) <- names(dem.df)

df = rbind(dem.df, rep.df)

df$Support = as.numeric(sub("%", "", df$Support))/100

df$Date = sub("[0-9]+\\s*–\\s*([0-9]+)", "\\1", df$Date)
df$Date = sub(".*–", "", df$Date)
df$Date = sub("[0-9]+\\s*-\\s*([0-9]+)", "\\1", df$Date)
df$Date = sub(".*-", "", df$Date)
df$Date = trimws(df$Date)
df$Date = as.Date(df$Date, format="%B %d, %Y")

df$Size = as.numeric(sub(",", "", df$Size))

df$Error = 1/sqrt(df$Size)

cols = c("#6666FF", "#333366", "#FF3333", "#993333")
labs = c("Clinton vs. Trump", "Sanders vs. Trump", "Trump vs. Clinton", "Trump vs. Sanders")

results = df

#breaks() returns n evenly spaced numbers between x and y
#whose squares are divisible by p
#the function is used for the legend
breaks <- function(x, y, n, p) {
  x = sqrt(ceiling(as.integer(x^2) / p) * p)
  y = sqrt(floor(as.integer(y^2) / p) * p)
  s = seq(x, y, length.out=n)
  for (i in 2:(n-1)) {
    s[i] = sqrt(round(s[i]^2 / p) * p)
  }
  return(unique(s))
}

d = ggplot(results, aes(x=Date, y=Support,
                        colour=Candidate, linetype=Candidate, shape=Candidate,
                        size=1/Error, weight=1/Error)) +
  labs(title="Nationwide opinion polling for the 2016 U.S. presidential election") + 
  geom_point(alpha=0.7) + 
  geom_smooth(span=0.8, show.legend=F, alpha=0.2) + 
  scale_colour_manual(name="Candidate", values=cols, labels=labs) + 
  scale_shape_manual(name="Candidate", values=c(16, 15, 16, 15), labels=labs) + 
  scale_linetype_manual(name="Candidate", values=c(1, 5, 1, 5), labels=labs) + 
  scale_size_area(max_size=3,
                  breaks=function(x) breaks(x[1], x[2], 5, 100), #5 numbers divisible by 100
                  labels=function(x) comma_format()(x^2),
                  name="Sample Size") + 
  scale_y_continuous(breaks=seq(0,1,0.05), minor_breaks=seq(0,1,0.01), labels=percent,
                     limits=c(0.34, 0.6)) + 
  scale_x_date(labels=date_format("%b %d"),
               breaks=sort(c(seq(as.Date("2016/1/1"), as.Date("2016/10/1"), "month"),
                             as.Date("2016/11/8")))) +
  theme(panel.grid.minor=element_line(size=0.2),
        panel.grid.major=element_line(size=0.6))

#save plot as "us2016.svg"
svg(filename="us2016.svg", 
    width=9, 
    height=5, 
    pointsize=12,
    bg="transparent")
d
dev.off()