Try this:

 D(parse(text = foo), "x")

On Thu, Dec 9, 2010 at 2:59 PM, Oleksandr Dyklevych <diklevich@gmail.com>wrote:

> Hi!
>
> I'm faced the next problem:
> suppose I have a vector of some coefficient and for some purpose from these
> coefficients I need dynamically build a functional expression (because, the
> number of elements in the vector of coefficients might differ each time).
> So, I'm trying to do like this (let the number of coefficients be 3):
>
> Building expression
>
>> foo <- gsub(",","*",toString(paste('(p',1:3,'*x + (1-p',1:3,'))',sep="")))
>> foo
>>
> [1] "(p1*x + (1-p1))* (p2*x + (1-p2))* (p3*x + (1-p3))"
>
> But now, how can I take derivative of this expression w.r.t. "x"?
>
>  dfoo <- D(foo,"x") #doesn't work as well as
>> dfoo <- D(as.expression(foo),"x")
>>
>
> May be there are other ways to handle this kind of situation?
>
>
> Best regards,
> Oleksandr
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
>



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

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