A cause other than data based on standardized regression was identified.
It is that the manual command added with target <- at the left hand side.


C1 did not work but C2 did.
C1 target<-dredge(mig.stds,  subset  =  temp_max)

C2 dredge(mig.stds,  subset  =  temp_max)

Elaine

On Wed, Aug 18, 2010 at 5:37 PM, elaine kuo <elaine.kuo.tw@gmail.com> wrote:

>
>> >
>> Please suggest how to define subset in my case
>>
>> How would I know? I still haven't seen your data. You seem to be
>> mistaken on what is and is not included in your model and you fitted it.
>> What hope do we have...? However, given the model 'mig.stds' from above
>> in this email:
>>
>> > mig.stds <-lm(SummerM_ratio ~ temp_max + evi_mean + topo_var +
>> >              topo_mean + coast + Iso_index_0808,
>> >              ## now tell R were to find the variables in formula
>> >              data = datum.std)
>> > ## If you are fitting a Gaussian GLM it is better fitted with lm()
>>
>> If you want to consider dredged models containing temp_max, then you
>> would do
>>
>> dredge(mig.stds, subset = temp_max)
>>
>> If you want models that contain temp_max and coast, then you'd do
>>
>> dredge(mig.stds, subset = temp_max & coast)
>>
>> or
>>
>> dredge(mig.stds, fixed = ~ temp_max + coast)
>>
>> The bits you include in subset or fixed are the names of your variables
>> that you want in or out of the models. In your case, the names of the
>> variables as input into the model formula. With 'subset' you need to use
>> logical operators (and [&], or [|]) whilst with 'fixed' you can specify
>> a formula of variables that should be included or excluded in the same
>> way you'd write any R formula.
>>
>> But, now having been told this, please note that this is *all* discussed
>> on the ?dredge help page if you bother to read it. I've never used this
>> package, and, OK, I have used R for going on for 11 or 12 years now so
>> am used to reading help pages and understand the language a bit more you
>> perhaps do, but you do seem to be asking questions or running into
>> problems that are all covered by the help pages.
>>
>> => I posted it for help, after following the manual with the command
>> dredge but receiving an error message two days ago.
>>
>
>
>>  command   target<-dredge(mig.stds,  subset  =  temp_max)
>>
>    error  in eval(expr, envir, enclos) : 'temp_max' not found
>
>  One possible cause could be data = datam.std.
>  datam.std was produced as the code below, which seemed to make it hard to
> find explanatory variables.
>  Please kindly share your experience in R, because I am unsure if my
> assumption is logical or not.
>
> Also, please kindly advise how to modify the command for dredging subset if
> possible.
> ( command   target<-dredge(mig.stds,  subset  =  temp_max))
> Thank you in advance.
>
> Elaine
>
> code
> library(MuMIn)
> datam <-read.csv("c:/migration/Mig_ratio_20100817.csv",header=T,
> row.names=1)
>
>  # std regression model (16 indep. variables)
>   datam.sd<-scale(datam)
>   datam.std<-as.data.frame(datam.sd)
>   summary (datam.std)
>   mean(datam.std)
>
> # obtain standard deviation
>     sd(datam.std)
>
>     mig.stds
> <-lm(SummerM_ratio~temp_ran+temp_mean+temp_max+temp_min+evi_ran+evi_mean+evi_max+evi_min+prec_ran+prec_mean+prec_max+prec_min+topo_var+topo_mean+coast+Iso_index_0808,data=datam.std)
>
>     summary(mig.stds)
>
>
>
>

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