[R] Indexing by logical vectors

[Christian Raschke]

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

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