I have noticed an interesting behavior when comparing how the base
plot() function deals with a data argument that downloads data from the
internet vs. how xyplot() in lattice performs the same task.
The goal is to plot hourly temperature data. The data is downloaded and
formatted for R using the function cimishourly() in the package cimis.
There is a line within the function that outputs the name of the file
being downloaded using cat().
When using plot() to plot the data, the following is written to the console:
library(cimis)
plot(air_temp ~ datetime, data = cimishourly("006"))
Downloading: ftp://ftpcimis.water.ca.gov/pub/hourly/hourly006.csv
Downloading: ftp://ftpcimis.water.ca.gov/pub/hourly/hourly006.csv
When using xyplot() to perform the same plot, the data is only
downloaded once:
library(lattice)
xyplot(air_temp ~ datetime, data = cimishourly("006"))
Downloading: ftp://ftpcimis.water.ca.gov/pub/hourly/hourly006.csv
Is this caused by a difference in how the two functions evaluate the
data argument?
Even more interesting, when adding a type = "l" argument to plot, the
data is downloaded 3 times.
Thank you for your time,
Greg
--
Greg Hirson
ghir...@ucdavis.edu
Graduate Student
Agricultural and Environmental Chemistry
1106 Robert Mondavi Institute North
One Shields Avenue
Davis, CA 95616
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