File:NZ Elections 2005-2008 - party bias.png

rm(list=ls())
#Load the complete HTML file into memory
html <- readLines(url("http://en.wikipedia.org/wiki/Opinion_polling_for_the_New_Zealand_general_election,_2008"),encoding="UTF-8")
closeAllConnections()
#The third table is the opinion poll data
tbl <- html[(grep("<table.*",html)[3]):(grep("</table.*",html)[3])]
#Now split it into the rows, based on the <tr> tag
tbl.rows <- split(tbl,cumsum(tbl=="<tr>"))
#Now extract the data
survey.dat <- lapply(tbl.rows,function(x) {
  #Start by only considering where we have <td> tags
  td.tags <- x[grep("<td",x)]
  #Polling data appears in columns 3-10
  dat     <- td.tags[3:10]
  #Now strip the data and covert to numeric format
  dat     <- gsub("<td>|</td>","",dat)
  dat     <- gsub("%","",dat)
  dat     <- gsub("-","0",dat)
  dat     <- as.numeric(dat)
  #Getting the date strings is a little harder. The approach we will take is to take advantage
  #of the title="date" hyperlinks to generate a set of dates
  date.str <- td.tags[2]                        #Dates are in the second column
  date.str <- gsub("<sup.*</sup>","",date.str)   #Throw out anything between superscript tags, as its an reference to the source
  titles <- gregexpr("(?U)title=\".*\"",date.str,perl=TRUE)[[1]]    #Find the location of the title tags
  #Now, extract the actual date strings
  date.strings <- rep(NULL,length(titles))
  for(i in 1:length(titles)) {
        date.strings[i] <- substr(date.str,titles[i]+7,titles[i]+attr(titles,"match.length")[i]-2)
  }
  yr <- rev(date.strings)[1]  
  dates <- rep(as.POSIXct(Sys.time()),length(date.strings)-1)
  for(i in 1:(length(date.strings)-1)) {
        dates[i] <- as.POSIXct(strptime(paste(date.strings[i],yr),"%B %d %Y"))
  }
  survey.time <- mean(dates)
  #Get the name of the survey company too
  survey.comp <- td.tags[1]
  survey.comp <- gsub("<sup.*</sup>","",survey.comp)  
  survey.comp <- gsub("<td>|</td>","",survey.comp)  
  survey.comp <- gsub("<U+2013>","-",survey.comp,fixed=TRUE)  
  survey.comp <- gsub("(?U)<.*>","",survey.comp,perl=TRUE)
  #And now return results
  return(data.frame(Company=survey.comp,Date=survey.time,t(dat)))
})

#Combine results 
surveys <- do.call(rbind,survey.dat)
colnames(surveys) <- c("Company","Date","Labour","National","NZ First","Maori Party","Greens","ACT","United Future","Progressive")

#Restrict plot(manually) to parties which have been over 5%
parties <- c("Greens","Labour","National","NZ First")
cols    <- c("darkgreen","red","blue","black")
polls   <- surveys[,c("Company","Date",parties)]
polls <- subset(polls,!is.na(surveys$Date))
polls$Date  <- as.double(polls$Date)
ticks <- ISOdate(c(2005,rep(2006,3),rep(2007,3),rep(2008,3)),c(9,rep(c(1,5,9),3)),1)
xlims <- range(as.double(c(ticks,ISOdate(2009,3,1))))
png("NZ_opinion_polls_2005-2008 -2.png",width=778,height=487,pointsize=16)
par(mar=c(3,4,1,1))
matplot(polls$Date,polls[,parties],pch=NA,xlim=xlims,ylab="Party support (%)",xlab="",col=cols,xaxt="n",ylim=c(0,60))
abline(h=seq(0,95,by=5),col="lightgrey",lty=3)
abline(v=as.double(ticks),col="lightgrey",lty=3)
#Now add loess smoothers
smoothed <- list()
for(i in 1:length(parties)) {
  smoother <- loess(polls[,parties[i]] ~ polls[,"Date"],span=0.33)
  smoothed[[i]] <- predict(smoother,se=TRUE)
  polygon(c(polls[,"Date"],rev(polls[,"Date"])),
    c(smoothed[[i]]$fit+smoothed[[i]]$se.fit*1.96,rev(smoothed[[i]]$fit-smoothed[[i]]$se.fit*1.96)),
    col=rgb(0.5,0.5,0.5,0.5),border=NA)
}
names(smoothed) <- parties
for(i in 1:length(parties)) {
  lines(polls[,"Date"],smoothed[[i]]$fit,col=cols[i],lwd=2)
}
matpoints(polls$Date,polls[,parties],pch=20,col=cols)
legend("topleft",legend=parties,col=cols,pch=20,bg="white",lwd=2)
axis(1,at=as.double(ticks),labels=format(ticks,format="%b\n%Y"),cex.axis=0.8)
axis(4,at=axTicks(4),labels=rep("",length(axTicks(4))))
#Add best estimates
for(i in 1:length(smoothed)) {
  lbl <- sprintf("%4.1f%% ± %2.1f",round(rev(smoothed[[i]]$fit)[1],1),round(1.96*rev(smoothed[[i]]$se.fit)[1],1))
  text(rev(polls$Date)[1],rev(smoothed[[i]]$fit)[1],labels=lbl,pos=4,col=cols[i])
}
dev.off()

#As a cross validation, print the rows where there are NA's
checks <- subset(surveys,apply(surveys,1,function(x) any(is.na(x))))
print(checks)

#Now, lets look at the poll residuals by party
#First, restack everything into a single long list
resid.dat <- data.frame(Company=NULL,Date=NULL,party=NULL,data=NULL,fit=NULL)
for(part in parties) {
  resid.dat <- rbind(resid.dat,data.frame(polls[,c("Company","Date")],party=part,data=polls[,part],fit=smoothed[[part]]$fit))
}
#Calculate residuals
resid.dat$bias <- (resid.dat$data-resid.dat$fit)/resid.dat$fit
#Prepare for plotting
plot.dat <- resid.dat[-which(resid.dat$Company=="2005 election result"),] 
replacements <- data.frame(old=c("TV3-TNS","One News-Colmar Brunton","Herald-DigiPoll","Roy Morgan Research",
                      "UMR Research","Fairfax Media Poll","Fairfax Media-Nielsen"),
                      new=c("TNS","Colmar\nBrunton","Digi-\nPoll","Roy\nMorgan",
                      "UMR","Nielsen","Nielsen"))
for(i in 1:nrow(replacements)) {
  plot.dat$Company <- gsub(replacements$old[i],replacements$new[i],plot.dat$Company,fixed=TRUE)
}

plot.dat$Company <- factor(plot.dat$Company)

#Plot bias vs party for each company figure
library(lattice)
plot.dat$Company <- gsub("\n"," ",plot.dat$Company)
p<-bwplot(bias*fit~party|Company,data=plot.dat,as.table=TRUE,
      scales=list(alternating=c(1)),
      xlab="Party",
      ylab="Absolute Bias (%)",
      fill=gsub("black","darkgrey",cols),
      panel=function(...) {
        panel.abline(h=0)
        tmp <-list(...)
        tmp <-split(tmp$y,factor(tmp$x))
        sig.diff <-sapply(tmp,function(x){
                    (1-pt(abs(mean(x))/sd(x),df=length(x)-1))*2 < 0.05
                                  
        }) 
#        fill.col <- ifelse(cols[panel.number()]=="black","darkgrey",cols[panel.number()])
#        fill.col <- ifelse(sig.diff,fill.col,NA)
        panel.bwplot(...,pch="|")},
      par.settings = list(box.rectangle=list(col="black",lty=1),
                          box.umbrella=list(col="black",lty=1),
                          plot.symbol=list(col="black")))
print(p)
png("NZ Elections 2005-2008 - party bias by company.png",width=600,height=600)
plot(p)
dev.off()

#Biases by party, with p values
biases <- tapply(plot.dat$bias,list(plot.dat$Company,plot.dat$party),FUN=mean)
p.values    <- tapply(plot.dat$bias,list(plot.dat$Company,plot.dat$party),FUN=function(x){
                    (1-pt(abs(mean(x))/sd(x),df=length(x)-1))*2})
print(round(biases*100,1))
print(round(p.values,3))