[R] How to plot 3-D surface graph from lmer mixed models?

Duncan Murdoch murdoch at stats.uwo.ca
Fri Aug 14 02:07:30 CEST 2009

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
>model at 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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