[R] Creating a Model Matrix - keeping NAs

[Rachel Cunliffe]

I am wanting to create a model matrix and keep the NAs.

stratmat <- model.matrix(myformula,mydata)

Is there any way to do this?  model.matrix doesn't have na.action as a
parameter.  Elsewhere I have made use of na.keep <- function(x){x}.

Many thanks,

Rachel Cunliffe

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