R/pvsRequest.R

In umatter/pvsR: Interact with the Project Vote Smart API for Scientific Research

pvsRequest <-
	function (request,inputs) {
		pvs.key <- getPVS_key()
    pvs.url <- paste("http://api.votesmart.org/",request,"key=",pvs.key,inputs,sep="") #generate url for request
		
		httpresp <- GET(url=pvs.url)
		xmltext <- content(x=httpresp, as="text")
		errors <-  getXMLErrors(xmltext) # check if xml can be parsed properly
		
		if (length(errors) != 0) {
			if (names(errors[[1]]$code) == "XML_ERR_CDATA_NOT_FINISHED") { # if not, try to fix 
				xmltext <- gsub(pattern="\003", replacement="", x=xmltext, fixed=TRUE)
			}
		}
		output.base <- xmlRoot(xmlTreeParse(xmltext, useInternalNodes=TRUE))
		
		if (names(output.base)[1]=="errorMessage") {
			
			# if the requested data is not available, return an empty (NA) data frame and give a warning
			warning(gsub(pattern="&", replacement=" ", x=paste("No data available for: ", inputs,". The corresponding rows in the data frame are filled with NAs.", sep=""), fixed=TRUE), call.=FALSE)
			output.df <- data.frame(matrix(nrow=1,ncol=0), stringsAsFactors = FALSE)
			
			return(output.df)
		} else {
			output <- t(unlist(xmlSApply(removeChildren(output.base,kids=1), function(x) unlist(xmlSApply(x, xmlValue), recursive = FALSE)), recursive = FALSE))
			output.df <- data.frame(output, row.names=NULL, stringsAsFactors = FALSE)
			names(output.df) <- gsub(".text", "", names(output.df), fixed = TRUE)
			
			return(output.df)
		}
	}