[R] file input with readLines

[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:
> 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.
>
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