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file input with readLines

2 messages · Cable, Sam B Civ USAF AFMC AFRL/RVBXI, R. Michael Weylandt

Cable, Sam B Civ USAF AFMC AFRL/RVBXI
# 
More on my previous question ...

I have put in timing statements to try to get a better idea of where the
problem is, like so:

conn<-file('filename','r')

for (chunk in 1:100000) {
   print(paste('begin read at',date()))
   Lines<-readLines(conn,n=25)
   print(paste('begin processing at',date()))
  # process "Lines"
   print(paste('end loop at',date()))
}

Every time I go through the loop, all the date() functions return
*exactly* the same time!  It *looks like* it runs through each iteration
very quickly and then takes longer and longer to simply start the next
iteration.  I don't believe this.  I think R must be doing some kind of
latency trick or something.  But, anyway, the point is that I was
assuming the problem was in the I/O, and now I don't know if it's I/O or
processing.  Either way, I don't understand it and would really
appreciate some wisdom from you guys.

Thanks.
R. Michael Weylandt
# 
If you are using rbind() at each iteration, that can slow things down
greatly. Look up a document called the R Inferno which discusses this
in great detail in circle 2.

Michael Weylandt

On Mon, Oct 3, 2011 at 2:26 PM, Cable, Sam B Civ USAF AFMC AFRL/RVBXI
<Sam.Cable at kirtland.af.mil> wrote: