[R] unexpected subset select results?

[David Winsemius]

On Aug 23, 2010, at 5:51 PM, ivo welch wrote:

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

You have created a perfect example for why it is a bad idea to attach  
data.frames.

?attach     # yes, I am yet again saying: "read the help page..."

... especially the 4th paragraph of the Details section.

-- 
David.



David Winsemius, MD
West Hartford, CT