R help - Jan 2011 - get() within a command, specifically lmer

Hello all.  Why doesn't this work?

d=data.frame(y=rpois(10,1),x=rnorm(10),z=rnorm(10),grp=rep(c('a','b'),each=5))
library(lme4)
model=lmer(y~x+z+(1|grp),family=poisson,data=d)
update(model,~.-z)###works, removes z
var='z'
update(model,~.-get(var))##doesn't remove z
update(model,~. -get(var,pos=d))###doesn't remove z

I am trying to remove z from the model in the update, but I can't do it
using get(), which is what I would like to do for a more complicated
program.  There's something about environments and get() that I don't
understand.

Any suggestions?

Thanks.

	[[alternative HTML version deleted]]

Formula syntax is different from regular syntax, it is "quoted" and
not evaluated in the same way as regular commands (otherwise operations like
'+' and '-' would do very different things).

For what you are trying to do, I would suggest creating the formula as a string
using paste or sprintf, then use as.formula on that string.  You can also use
the substitute function, but that tends to be a bit more complicated.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Patrick McKann
> Sent: Wednesday, January 05, 2011 8:26 AM
> To: r-help at r-project.org
> Subject: [R] get() within a command, specifically lmer
> 
> Hello all.  Why doesn't this work?
> 
>
d=data.frame(y=rpois(10,1),x=rnorm(10),z=rnorm(10),grp=rep(c('a','b'),e
> ach=5))
> library(lme4)
> model=lmer(y~x+z+(1|grp),family=poisson,data=d)
> update(model,~.-z)###works, removes z
> var='z'
> update(model,~.-get(var))##doesn't remove z
> update(model,~. -get(var,pos=d))###doesn't remove z
> 
> I am trying to remove z from the model in the update, but I can't do it
> using get(), which is what I would like to do for a more complicated
> program.  There's something about environments and get() that I
don't
> understand.
> 
> Any suggestions?
> 
> Thanks.
> 
> 	[[alternative HTML version deleted]]
> 
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