google-scraper.R

## Load libraries
library(XML)
library(dplyr)
library(RCurl)

## Get the results for a specific term
scrape_term = function(search_term,npages){
  base_url = "http://scholar.google.com/scholar?"
  search_string = paste0("q=",paste0(strsplit(search_term," ")[[1]],collapse="+"))
  dat = data.frame(NA,nrow=10*npages,ncol=3)
  names(dat)=c("pub_year","cites","title")
  for(i in 1:npages){
    if(i==1){
      url1 = paste0(base_url,search_string)
    }else{
      start_string = paste0("&start=",(i-1)*10)
      url1 = paste0(base_url,search_string,start_string)
    }
  doc <- htmlParse(url1,encoding="UTF-8")
  titles <- xpathSApply(doc, "//h3[@class='gs_rt']", xmlValue)
  cites = xpathSApply(doc,
                    '//*[contains(concat( " ", @class, " " ), concat( " ", "gs_ri", " " ))]//*[contains(concat( " ", @class, " " ), concat( " ", "gs_fl", " " ))]//a[(((count(preceding-sibling::*) + 1) = 1) and parent::*)]',
                    xmlValue)

  cites = cites[1:10*3-2]
  cites = as.numeric(sapply(cites,function(x){strsplit(x,"Cited by ")[[1]][2]}))
  pub <- xpathSApply(doc, "//div[@class='gs_a']", xmlValue)
  pub_years =  as.integer(gsub(".*\\s(\\d{4})\\s.*", "\\1", pub))
  ind = ((i-1)*10+1):(i*10)
  dat[ind,1] = pub_years
  dat[ind,2] = cites
  dat[ind,3] = titles
  }
  return(dat)
}


## Search for these terms
terms = c('empirical processes','proportional hazards model','generalized linear model','semiparametric','generalized estimating equation','false discovery rate','microarray statistics','lasso shrinkage','rna-seq statistics')

nterms=length(terms)

term_data = vector(mode="list",length=nterms)
npages =3
for(i in 1:length(terms)){
  term_data[[i]] = scrape_term(terms[i],npages)
  term_data[[i]] = cbind(term_data[[i]],rep(terms[i],npages*10))
  names(term_data[[i]])[4] = "term"
  Sys.sleep(3)
  cat(i)
}

term_vec = as.vector(sapply(term_data,function(x){x$term}))

## Put the term factor in order for the boxplot
term_vec = reorder(term_vec,rep(1:9,each=30))

## Make the axis abbreviated by changing labels
levels(term_vec) = c("Emp. Proc.", "Prop. Haz.", "GLM", "Semi-param.","GEE","FDR","microarray","lasso","rna-seq")
pubyear_vec = as.vector(sapply(term_data,function(x){x$pub_year}))
title_vec = as.vector(sapply(term_data,function(x){x$title}))


## Create the plot
png(file="citations-boxplot.png",height=400,width=600)
par(bg="black",fg="white",col.axis="white",
    col.lab="white",col.main="white",
    mar=c(6,4,4,2))
boxcol = "#20B2E3"
pointcol="white"
tmp = boxplot(pubyear_vec ~ term_vec2)
grid(nx=NA, ny=NULL)
boxplot(pubyear_vec ~ term_vec2,col=boxcol, 
        bty="n",xaxt="n",yaxt="n",ylab="year",main="Publication Year of First 30 G.S. Hits",frame.plot=FALSE)
stripchart(pubyear_vec ~ term_vec2,vertical=T,method="jitter",add=TRUE,pch=19,col=pointcol,cex=0.5)
axis(side=1,at=1:length(tmp$names),labels=tmp$names,tick=FALSE,las=2)
axis(side=2,at=at2,tick=FALSE)
add_simply_logo("black")
dev.off()

tapply(pubyear_vec,term_vec,function(x){mean(x,na.rm=T)})

There is an issue with the XML package. A workaround would be
library(httr)
doc <- htmlParse(rawToChar(GET(url)$content))