[R] obtaining output from an evaluated expression

Jack Bowden jack.bowden at mrc-bsu.cam.ac.uk
Fri Dec 19 11:09:33 CET 2008


I am trying to use the deriv and eval functions to obtain the value of a 
function , say  "xi-(alpha0+alpha1*gi)" , differentiated with respect to 
alpha0 and alpha1, in the following way

# for gi = 0

 > dU1dtheta  <- deriv(~ xi-(alpha0+alpha1*gi), c("alpha0","alpha1")) 
 > eval(dU1dtheta)
     alpha0 alpha1
[1,]     -1      0

I want to extract the output gradient values of -1 and 0 but I don't 
know how to access them. The only thing I can access is the intercept  
term via.

 > eval(dU1dtheta)[1].

I'm sorry if this is too basic a question for the list, but any help 
would be greatly appreciated


Dr Jack Bowden
MRC Biostatistics Unit
Institute of Public Health
Forvie Site
Robinson Way

Tel: (01223) 330385

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