willow1980 wrote:
Dear Professor Murdoch,
That is exactly the difficulty for me. I don't know how to make a prediction
with lmer using "expand.grid"; at the moment, I can use
“mo...@x%*%fixef(model)” to get predicted values for existing observational
data, but not data by "expand.grid". Actually, if I know this, I can then
use "persp" or "wireframe" to plot 3-D surface graph. Do you know or have
available code for this aim?
No, I've never used lmer.
Duncan Murdoch
Sorry, this request must sound very lazy or stupid.
Thank you very much for helping!
Best regards,
Duncan Murdoch-2 wrote:
I only see two explanatory variables: afr_c, byear_c. If you have more
than two, you can't use a surface plot: surfaces are two dimensional.
All of the 3D surface functions want basically the same thing: a matrix
giving evaluations of a function at locations of the explanatory
variables. So you need to calculate that. I'd do it by using
expand.grid to create a large set of combinations of values of the
explanatory variables, ask your model to do predictions at all of those
locations, and then reshape the result into a matrix.
Duncan Murdoch
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