[R] symbolic matrix elements...
Duncan Murdoch
murdoch at stats.uwo.ca
Mon Sep 18 19:52:47 CEST 2006
On 9/18/2006 1:16 PM, Evan Cooch wrote:
>
> Eik Vettorazzi wrote:
>> test=matrix(c( expression(x^3-5*x+4), expression(log(x^2-4*x))))
>> works.
> Well, not really (or I'm misunderstanding). Your code enters fine (no
> errors), but I can't access individual elements - e.g., test[1,1] gives
> me an error:
>
> > test=matrix(c( expression(x^3-5*x+4), expression(log(x^2-4*x))))
> > test[1,1]
> Error: matrix subscripting not handled for this type
>
> Meaning...what?
Matrices in R are just vectors with a dim attribute. The matrix
function let you create the matrix, but the [ function doesn't know what
to do when the vector is of mode expression.
This is an unimplemented case, a limitation (or perhaps bug if it wasn't
intentional) in R.
>> btw. you recieved an error because D expects an expression and you
>> offered a list
>
> OK - so why then are each of the elements identified as an expression
> which I print out the vector? Each element is reported to be an
> expression. OK, if so, then I remain puzzled as to how this is a 'list'.
The problem is that if m is a list, then m[1] is a list with one
element. You wanted m[[1]] to extract the first element and get
something that's not a list.
Duncan Murdoch
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