model.matrix and missing values

Hi,

Does anyone know an easy way of retaining rows in a model.matrix where  
missing values are present in the predictors.  Ideally I'd be able to  
retain these rows as zeros.

Thanks,

Jarrod
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
Dear Jarrod,

If you use na.action=na.exclude in fitting the model, then you can produce
rows of NAs in the model matrix with na.resid(); e.g., for a model m,

	mm <- naresid(m$na.action, model.matrix(m))

Then if you really want to convert the rows of NAs in mm to 0s, you could
use

	mm[is.na(mm)] <- 0

I hope this helps,
 John

------------------------------
John Fox, Professor
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
web: socserv.mcmaster.ca/jfox
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of Jarrod Hadfield
Sent: December-28-08 8:13 AM
To: r-help at r-project.org
Subject: [R] model.matrix and missing values

Hi,

Does anyone know an easy way of retaining rows in a model.matrix where
missing values are present in the predictors.  Ideally I'd be able to
retain these rows as zeros.

Thanks,

Jarrod

--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.

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