R help - Jan 2007 - eval while keeping NA-s

Dear R-people,

I would like to construct a model frame while keeping eventual NA-s in
it.  The code looks like in lm():

   m <- match(c("formula", "data", "subset",
"weights", "na.action",
                "offset"), names(mf), 0)
   mfO <- mf[c(1, m)]
   mfO$drop.unused.levels <- TRUE
   mfO[[1]] <- as.name("model.frame")
   names(mfO)[2] <- "formula"
   mfO <- eval(mfO, parent.frame())

The problem is that eval() removes all the observation which include
NA-s.  

Are there ways to get the frames and keep NA-s?  I see, I can play
around with the "na.action" attribute of the resulting frame, but how
can I set the na.action?

Thanks in advance,
Ott

On Thu, 18 Jan 2007, Ott Toomet wrote:
> Dear R-people,
>
> I would like to construct a model frame while keeping eventual NA-s in
> it.  The code looks like in lm():
>
>   m <- match(c("formula", "data",
"subset", "weights", "na.action",
>                "offset"), names(mf), 0)
>   mfO <- mf[c(1, m)]
>   mfO$drop.unused.levels <- TRUE
>   mfO[[1]] <- as.name("model.frame")
>   names(mfO)[2] <- "formula"
>   mfO <- eval(mfO, parent.frame())
>
> The problem is that eval() removes all the observation which include
> NA-s.
>
> Are there ways to get the frames and keep NA-s?  I see, I can play
> around with the "na.action" attribute of the resulting frame, but
how
> can I set the na.action?
Set na.action=na.pass on the call, or reset in your code (as that resets 
drop.unused.levels).


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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