[R] unexpected subset select results?

[Gavin Simpson]

On Mon, 2010-08-23 at 17:51 -0400, ivo welch wrote:
> quizz---what does this produce?

Henrique has provided an answer to the question, but...

>    d=data.frame( a=1:1000, b=2001:3000, z= 5001:6000 )
>    attach(d); c <- (a+b)>25; detach(d)

...this is ugly and will potentially catch you out one day if you forget
to detach. These three calls can be achieved using a single with() :

c <- with(d, (a + b) > 25)

And the version you wanted:

attach(d); d$c <- (a+b)>25; detach(d)

can be done using within():

d <- within(d, c <- (a + b) > 25)

and with the latter, the intention is pretty clear.

HTH

G

>    d= subset(d, TRUE, select=c( a, b, c ))
> 
> yes, I know I have made a mistake, in that the code does not do what I
> presumably would have wanted.  it does seem like unexpected behavior,
> though, without an error.  there probably is some reason why this does
> not ring an alarm bell...
> 
> /iaw
> ----
> Ivo Welch (ivo.welch at brown.edu, ivo.welch at gmail.com)
> 
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