[R] different behavior of $ with string literal vs string variable as argument

[R. Michael Weylandt]

On Sun, Feb 10, 2013 at 9:06 PM, David Romano <dromano at stanford.edu> wrote:
> Hi everyone,
>
> I ran into the issue below while trying to execute a command of the form
>
> apply(list.names,1, function(x)  F(favorite.list$x) )
>
> where list.names is a character vector containing the names of the elements
> of favorite.list and F is some function defined on a list element.
>
> Namely,  the $ operator doesn't treat the string variable 'x' as the string
> it represents, so that, e.g.
>
>> ll <- list(ss="abc")
>> ll$ss
> [1] "abc"
>> ll$"ss"
> [1] "abc"
>
> but
>
>> name <- "ss"
>> ll$name
> NULL
>
> I can get around this by using integers and the [[ and [ operators, but I'd
> like to be able to use names directly, too -- how would I go about doing
> this?
>

You've already found it: the bracket operators....

MW

> Thanks for your help in clarifying what might be going on here.
>
> David
>
>         [[alternative HTML version deleted]]
>
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