> On Oct 7, 2016, at 10:44 AM, Jorge Cimentada <cimenta...@gmail.com> wrote:
>
> Hi Bert,
>
> Yes, I'm aware of the difference between a and "a" but in terms of object
> classes I don't see the difference between "a" and names(mtcars)[1].
> They're both strings.
They are not both "strings". One is a character value and the other is an
expression that requires two different function evaluations. Inside the call to
`c()`, the expressions on either side of an "="-sign are handled differently
than they are outside a matching set of function parentheses. I _think_ they
are parsed as 'alists', and teh which the ?alist page says the alist()-function
does not evaluate the LHS of a pair being formed by the "="-operator. I was,
however, not able to find descriptions of this in either The R Language
Definition or R Internals.
I see Duncan has pointed out that "a" is converted to an R symbol/name as a
"courtesy". There is some irony in the fact that the `names` function does not
return R names, which are language objects with mode name.
--
David
> However, for creating a named character vector, this
> works:
>
> c("a" = "b)
>
> But this doesn't
>
> c(names(mtcars)[1] = "b")
> For example:
>
> df <- data.frame("a" = 1:5)
> c("a" = "b")
> c(names(df)[1] = "b") # error
>
> But
>
> identical(names(df)[1], "a")
>
The `identical` function evaluates both its arguments.
> That was my initial question.
>
> [[alternative HTML version deleted]]
>
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David Winsemius
Alameda, CA, USA
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