[R] Indexing by logical vectors

[Christian Raschke]

On Mon, 2010-07-19 at 19:46 -0400, David Winsemius wrote:
> On Jul 19, 2010, at 7:16 PM, Christian Raschke wrote:
> 
> > Dear R-Listers,
> >
> > My question concerns indexing vectors by logical vectors that are  
> > based on the original vector. Consider the following simple example  
> > to hopefully make clear what I mean:
> >
> > a <- rnorm(10)
> > a[a<0] <- NA
> >
> > However, I am now working with multiple data frames that I received,  
> > where each of them has nicely descriptive, yet long names(). In my  
> > scripts there are many instances where operations similar to the one  
> > above are required. Again a simple example:
> >
> >
> > some.data.frame <- data.frame(some.long.variable.name=rnorm(10),  
> > some.other.long.variable.name=rnorm(10))
> >
> > some.data.frame$some.other.long.variable.name[some.data.frame 
> > $some.other.long.variable.name < 0] <- NA
> >
> >
> > The fact that the names are so long makes things not very readable  
> > in the script and hard to debug. Is there a way in R to refer to the  
> > "self" of whatever is being indexed? I am looking for something like
> >
> > some.data.frame$some.other.long.variable.name[.self < 0] <- NA
> 
> There is an alternative, "is.na()<-" which I think is a bit  more  
> readable:
> 
> is.na($some.other.long.variable.name) <- some.data.frame 
> $some.other.long.variable.name < 0

Thanks, David!

As written, this throws and error. However,

is.na(some.data.frame$some.other.long.variable.name) <- some.data.frame
$some.other.long.variable.name < 0

works, but does not seem like much of an improvement to me. 

> 
> But do _not_ do:
> 
> with(some.data.frame, is.na(some.other.long.variable.name) <-  
> some.other.long.variable.name < 0 )
>