Nothing
# fetch and format monthly data by course number, starting year, and ending year
CDECsnowQuery <- function(course, start_yr, end_yr) {
# construct the URL for the DWR website
u <- paste(
'http://cdec.water.ca.gov/cgi-progs/snowQuery?course_num=', course,
'&month=(All)&start_date=', start_yr,
'&end_date=', end_yr,
'&csv_mode=Y&data_wish=Retrieve+Data',
sep='')
# read the result of sending the URL as a CSV file:
# noting that it has a header,
# skipping the first line
# not converting characters to factors
# interpreting ' --' as NA
d <- read.csv(file=url(u), header=TRUE, skip=1, as.is=TRUE, na.strings=' --')
if(nrow(d) == 0 | ncol(d) != 5)
stop('query returned no data', call.=FALSE)
# compute the density, as percent
d$density <- (d$Water / d$Depth) * 100.0
# add SWE collumn using Adjusted if present
d$SWE <- ifelse(is.na(d$Adjusted), d$Water, d$Adjusted)
# convert date to R-friendly format
d$Meas.Date <- as.Date(d$Meas.Date, format="%d-%B-%Y")
# convert representative date
# note that this month isn't the same as the month when the data were collected
# note that we need to add an arbitrary 'day' to the string in order for it to be parsed correctly
d$Date <- as.Date(paste('01/', d$Date, sep=''), format="%d/%m/%Y")
# extract the year and month for reporting ease later
d$year <- as.numeric(format(d$Date, "%Y"))
d$month <- factor(format(d$Date, '%B'), levels=c('January','February','March','April','May','June','July','August','September','October','November','December'))
# return the result
return(d[, c('Meas.Date','Date','year','month','Depth','Water','Adjusted','SWE','density')])
}
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