#' Function to return data from the NWISWeb WaterML1.1 daily values service
#'
#' This function accepts a url parameter that already contains the desired
#' NWIS site, parameter code, statistic, startdate and enddate. It returns a
#' data frame containing "Date" and "Discharge"
#'
#' @param obs_url string containing the url for the retrieval
#' @return Daily a data frame containing columns 'Date' and 'Discharge'
#' @export
#' @examples
#' url<-"http://waterservices.usgs.gov/nwis/dv/?format=waterml,1.1&sites="
#' sites<-"02177000"
#' startdate<-"2012-09-01"
#' enddate<-"2012-10-01"
#' offering<-'00003'
#' property<-'00060'
#' obs_url<-paste(url,sites,'&startDT=',startdate,'&endDT=',enddate,'&statCd=',offering,'¶meterCd=',property,sep='')
#' getXMLWML1.1Data(obs_url)
getXMLWML1.1Data <- function(obs_url){
cat(paste("Retrieving data from: \n", obs_url, "\n", sep = " "))
obs_open <- file(obs_url,open="r")
content <- paste(readLines(obs_open,warn=FALSE))
close(obs_open,type="r")
if (length(content)>0) {
test <- capture.output(tryCatch(xmlTreeParse(content, getDTD=F, useInternalNodes=TRUE),"XMLParserErrorList" = function(e) {cat("incomplete",e$message)}))
} else {test<-0}
while (length(grep("<?xml",test))==0) {
obs_open <- file(obs_url,open="r")
content <- paste(readLines(obs_open,warn=FALSE))
close(obs_open,type="r")
if (length(content)>0) {
test <- capture.output(tryCatch(xmlTreeParse(content, getDTD=F, useInternalNodes=TRUE),"XMLParserErrorList" = function(e) {cat("incomplete",e$message)}))
} else {
test<-0
}
}
doc <- htmlTreeParse(content, asText=TRUE, useInternalNodes=TRUE)
values<-xpathSApply(doc, "//timeseries//value")
values2<-sapply(values,function(x) as.numeric(xmlValue(x)))
dateSet<-xpathSApply(doc, "//@datetime")
dateSet2<-sapply(dateSet,function(x) toString(substr(x,1,10)))
Daily<-as.data.frame(matrix(ncol=2,nrow=length(values2)))
colnames(Daily)<-c('date','discharge')
Daily$discharge<-values2
if (length(dateSet)>2) {
Daily$date<-as.Date(dateSet2)}
return (Daily)
}
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.