gistfile1.r

#install the packages
install.packages('XML')
require(XML)

#get raw html for Lake Minnetonka
html.raw<-htmlTreeParse(
    'http://www.dnr.state.mn.us/lakefind/showreport.html?downum=27013300',
    useInternalNodes=T
    )

#parse html using <p> tag    
html.parse<-xpathApply(html.raw, path="//p", fun=xmlValue)

#find elements that containt 'Depth'
robj.parse<-grep('*Depth*',unlist(html.parse),value=T)

#get correct element with maximum depth info
robj.parse<-robj.parse[[1]]

#use 'strsplit' to get actual value for maximum depth
depth.parse<-as.numeric(strsplit(strsplit(robj.parse,'ft): ')[[1]][2],'Water')[[1]][1])

#combine above code into a single function
depth.fun<-function(lake){

  url.in<-paste(
    'http://www.dnr.state.mn.us/lakefind/showreport.html?downum',
    lake,
    sep='='
    )
    
  html.raw<-htmlTreeParse(url.in,useInternalNodes=T)
      
  html.parse<-xpathApply(html.raw, path="//p", fun=xmlValue)
  
  robj.parse<-grep('*Depth*',unlist(html.parse),value=T)
  
  depth.parse<-as.numeric(strsplit(strsplit(robj.parse,'ft): ')[[1]][2],'Water')[[1]][1])
  
  return(depth.parse)
  
  }

#examples showing how the function is used  
depth.fun('27013300')

lake.ids<-c('27013700','82004600','82010400')
sapply(lake.ids,depth.fun)