Greetings -- coming from Python/Ruby perspective, I'm wondering about
certain features of R as a programming language.
Say I have a huge table t of the form
run ord unit words new
1 1 6939 1013 641
1 2 275 1001 518
1 3 3314 1008 488
1 4 14154 1018 463
1 5 2982 1006 421
Alternatively, it may have a part column in front. For each run (in
a part if present), I select ord and new columns as x and y and plot
their functions in various ways. t is huge. So I want to select the
subset to plot, as follows:
t.xy <- function(t,part=NA,run=NA) {
if (is.na(run)) {
# TODO does this entail a full copy -- or how do we do
references
in R?
r <- t
} else if (is.na(part)) {
r <- t[t$run == run,]
} else { # part present too
r <- t[t$part == part & t$run == run,]
}
x <- r$ord
y <- r$new
xy.coords(x,y)
}
What I'm wondering about is whether r <-t will copy the complete t,
and how do I minimize copying in R. I heard it's a functional
language -- is there lazy evaluation in place here?
Additionally, tried to use --args command line arguments, and found a
way only due to David Brahm -- who helped with several important R
points (thanks Dave!):
#!/bin/sh
# graph a fertility run
tail --lines=+4 "$0" | R --vanilla --slave --args $*; exit
args <- commandArgs()[-(1:4)]
...
And, still no option processing as in GNU long options, or python or
ruby's optparse.
What's the semantics of parameter passing -- by value or by reference?
Is there anything less ugly than
print(paste("x=",x,"y=",y))
-- for routine printing? Can [1] be eliminated from such simple
printing? What about formatted printing?
Is there a way to assign all of
a <- args[1]
b <- args[2]
c <- args[3]
in one fell swoop, a lá Python's
a,b,c = args
What's the simplest way to check whether a filename ends in ".rda"?
Will ask more as I go programming...
(Will someone here please write an O'Reilly's "Programming in R"? :)
Cheers,
Alexy
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