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

[Benjamin Tyner]

Duncan,

How embarrassing! Thanks.

-Ben

On 06/26/2014 10:25 PM, Duncan Murdoch wrote:
> On 27/06/2014, 4:08 AM, Benjamin Tyner wrote:
>> 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
>>
> Try replacing "Rscript -e" with "echo" to see what your shell is really
> sending as a command to execute.   I suspect it is treating $bar as a
> shell variable (see the error message, it has disappeared).
>


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