[R] non-interactive subset, `$`, and quotes

[Benjamin Tyner]

Hi

I know that subset() is not intended for use in programming. However I
am still curious to learn why, in non-interactive mode, if I take away
the quotes around 'bar'

   Rscript -e "foo <- list(bar = iris); head(subset(foo$'bar',
Species=='setosa'))"
     Sepal.Length Sepal.Width Petal.Length Petal.Width Species
   1          5.1         3.5          1.4         0.2  setosa
   2          4.9         3.0          1.4         0.2  setosa
   3          4.7         3.2          1.3         0.2  setosa
   4          4.6         3.1          1.5         0.2  setosa
   5          5.0         3.6          1.4         0.2  setosa
   6          5.4         3.9          1.7         0.4  setosa

then it results in an error:

   Rscript -e "foo <- list(bar = iris); head(subset(foo$bar,
Species=='setosa'))"
   Error in subset.default(foo, Species == "setosa") :
     object 'Species' not found
   Calls: head -> subset -> subset.default
   Execution halted

and also why this does not occur in interactive mode? My sessionInfo() is

   R Under development (unstable) (2014-06-26 r66043)
   Platform: x86_64-unknown-linux-gnu (64-bit)

   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=en_US.UTF-8    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

Regards
Ben