R script that should plot xts class data to a png file doesn't produce a png file - r

Question

I had a working script that used a loop to produce many png file plots of xts class data. Now the script throws an error and if I comment out the line throwing the error (a call to abline() ) then the script executes but without producing a png file. The issue seems to involve plotting xts class data and/or a loop or script.
Searching on stackoverflow didn't provide a solution or reference to this issue. I've reproduced the issue in the following example. In practice, the script would use different filenames within the loop and non-trivial data.
# put following code in 'myscript.R' and execute using source('myscript.R',print.eval=TRUE) or source('myscript.R')
# xts class data
data <- xts(seq(1:10),order.by=as.Date(seq(1:10)))
# a non xts version of same data
#data <- seq(1:10)
for(i in 1:1) {
filename <- 'myfile.png'
png(filename)
plot(data)
lines( (data-1),col='red')
abline(h=1)
dev.off()
}
# The call to abline in above script with xts class data gives error 'plot.new has not been called yet'
# If comment out the call to abline it completes but doesn't produce a png file
# script works fine with abline for non xts data

Answer 1

Using xts >= 0.10.1, this saves to file what you want
for(i in 1:1) {
filename <- 'myfile.png'
png(filename)
plot(data)
print(lines( (data-1),col='red', on = 1))
print(lines(xts(x = rep(1, NROW(data)), order.by = index(data)),col='green', on= 1) )
dev.off()
}
Use the print calls for the extra lines. I'd also use lines for the horizonal line, instead of abline, as this is more consistent with plotting with xts.
Also your error can be avoided if you do print(abline(h=1))