[R] indexing in data frames

[William Dunlap]

And if you are extremely concerned with speed, do
not compute a$b and a$c in every iteration of the loop.
E.g., change
   lapply(seq_along(a$c),function(x) a$b[x]-a$c[[x]])
to something like
   with(a, lapply(seq_along(c), function(x)b[x] - c[[x]]))

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of R. Michael Weylandt
> Sent: Thursday, August 09, 2012 4:22 PM
> To: arun
> Cc: R help; jimi adams
> Subject: Re: [R] indexing in data frames
> 
> On Thu, Aug 9, 2012 at 5:30 PM, arun <smartpink111 at yahoo.com> wrote:
> >
> >  lapply(1:length(a$c),function(x) a$b[x]-a$c[[x]])
> 
> Arun,
> 
> I've seen you use this idiom a few times lately and I'd just like to note that
> 
> seq_along()
> 
> is an (underutilized) primitive and a safer and faster alternative
> (avoiding the pathological length(x) = 0 case).
> 
> Cheers,
> Michael
> 
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