[R] Indexing by logical vectors

[David Winsemius]

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

But do _not_ do:

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

-- 
David.
>
> that would accomplish the same result as above. Or is there another  
> concise, but less messy way to do this? I prefer not attaching the  
> data.frames and partial matching makes things even more messy since  
> many names() are very similar. I know I could just rename  
> everything, but I'd like to learn if there is and easy or obvious  
> way to do this in R that I have missed so far.
>
> I would appreciate any advice, and I apologize if this topic has  
> been discussed before.
>
>
> > sessionInfo()
> R version 2.11.0 (2010-04-22)
> x86_64-redhat-linux-gnu
>
> locale:
> [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
> [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
> [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8
> [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
> [9] LC_ADDRESS=C               LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
>
> -- 
> Christian Raschke
> Department of Economics
> and
> ISDS Research Lab (HSRG)
> Louisiana State University
> crasch2 at lsu.edu
>
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David Winsemius, MD
West Hartford, CT