[R] "[.data.frame" and lapply

From: baptiste auguie <ba208_at_exeter.ac.uk>
Date: Wed, 25 Mar 2009 18:56:57 +0000

Dear all,

Trying to extract a few rows for each element of a list of data.frames, I'm puzzled by the following behaviour,

> d <- lapply(1:4, function(i) data.frame(x=rnorm(5), y=rnorm(5)))
> str(d)
> lapply(d, "[", i= c(1)) # fine, this extracts the first columns
> lapply(d, "[", j= c(1, 3)) # doesn't do nothing ?!
> library(plyr)
> llply(d, "[", j= c(1, 3)) # same

Am i misinterpreting the meaning of "j", which I thought was an argument of the method "[.data.frame"?

> args(`[.data.frame`)
> function (x, i, j, drop = if (missing(i)) TRUE else length(cols) ==
> 1)

Many thanks,


Baptiste Auguié

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,

Phone: +44 1392 264187


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