[R] Extracting formulae from expression() / deriv()

[Henrique Dallazuanna]

Try this:

attributes(eval(df1p))$gradient[,'P']


On Tue, Apr 6, 2010 at 9:09 AM, nickymcp <nickymcpherson at gmail.com> wrote:
>
> I am attempting to extract the derivative/ gradient from this expression
>
> df1p <- deriv(f1, "P")
>> df1p
> expression({
>    .value <- s - c - a * P
>    .grad <- array(0, c(length(.value), 1L), list(NULL, c("P")))
>    .grad[, "P"] <- -a
>    attr(.value, "gradient") <- .grad
>    .value
> })
>
> So in this case I want to extract the "-a".
>
> I have read the expression help file, which tells me that I should use [ and
> [[ to extract information, but the best result I've had so far is
>
>> df1p[attr(f1,"gradient")]
> expression()
>
> I'm sure I'm missing something really basic, but I've now lost several hours
> trying to do this and I'm getting pretty desperate.
> --
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> Sent from the R help mailing list archive at Nabble.com.
>
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>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O