[R] Error with predict and newdata

[David Winsemius]

On Aug 7, 2015, at 2:41 PM, kira taylor wrote:

> Hi!
> 
> I am trying to use predict to apply my model to data from one time period to
> see what might be the values for another time period.  I did this
> successfully for one dataset, and then tried on another with identical code
> and got the following error:
> 
> Error in eval(predvars, data, env) :
>  numeric 'envir' arg not of length one
> 
> The only difference between the two datasets was that my predictor model for
> the first dataset had two predictor variables and my model for the second
> dataset had only one.  Why would this make a difference?
> 
> My dougfir.csv contains just two columns with thirty numbers in each,
> labeled height and dryshoot.
> 
> my lm is: fitdougfir <- lm(dryshoot~height,data=dougfir)
> 
> It gets a little complicated (and messy, sorry!  I am new to R) because I
> then made a second .csv - the one I used to make my model contained values
> from just June.  My new .csv (called alldatadougfir.csv) includes values
> from October as well, and also contains a "date" column that labels the
> values either "june" or "october."
> 
> I did the following to separate the height data by date:
> 
> alldatadougfir[alldatadougfir$date=="june",c("height")]->junedatadougfir
> alldatadougfir[alldatadougfir$date=="october",c("height")]->
> octoberdatadougfir

Those are no longer lists or dataframe, which are the proper classes of object to pass to predict. 

-- 
David.
> 
> I then want to use my June model to predict my October dryshoots using
> height as my variable and I did the following:
> 
> predict(fitdougfir, newdata=junedatadougfir)
> predict(fitdougfir, newdata=octoberdatadougfir)
> 
> Again, I did this with an identical dataset successfully - the only
> difference was that my model in the successful dataset had two predictor
> variables instead of the one variable (height) I have in this dataset.
> 
> Sorry again for my messy code!
> 
> Thank you very much,
> 
> Kira
> 
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> 
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David Winsemius
Alameda, CA, USA