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# Read XML data using a low-level streaming model to be able to handle
# very large data.
# We'll just pick out Total Time
# Use a modified version if iTunes format to make it a less generic format.
#Need a state machine
#Whenever we see the start of an XML element named Total_Time,
#prepare to store the next pieces of text
#Then when we see the end of the Total_Time, stop collecting.
create =
function(verbose = FALSE)
{
times <- character()
inTotalTimeElement = FALSE
# called for start of <Total_Time> element,
# so always set inTotalTime to TRUE
tt = function(name, ...) {
if(verbose) cat("In tt\n")
inTotalTimeElement <<- TRUE
}
# If we are in a Total_Time element,
# put the x into the times vector
collect = function(x) {
if(verbose) cat("in collect\n")
if(inTotalTimeElement)
times <<- c(times, x)
}
# Need to turn inTotalTimeElement off if it is on.
endElement = function(name, ...) {
# if(name == "Total_Time")
if(verbose) cat("end Total_Time\n")
inTotalTimeElement <<- FALSE
}
# return a list of functions which are used by the SAX parser
# and also .result which gives us the values
list("Total_Time" = tt,
"/Total_Time" = endElement,
.text = collect,
.result = function()
as.numeric(times))
}
#
if(FALSE) {
h = create(verbose = TRUE)
o = xmlEventParse("http://eeyore.ucdavis.edu/itunes-short.xml", handlers = h, saxVersion = 2)
h$.result()
}
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