[R] Reading data from a dataframe

[Duncan Murdoch]

On 09/02/2008 11:38 AM, David Winsemius wrote:
> "Alexander Ovodenko" <ovodenko at princeton.edu> wrote in
> news:85e440020802090820n281dfffcwffee2807cb483a6e at mail.gmail.com: 
> 
>> Thanks for the replies to my prior question.  My problem is that R
>> always says object not found when I enter a variable name into a
>> command.  I converted a Stata file into an Rdata file by first
>> loading the foreign package by entering
>>
>> require(foreign)
>>
>> Then I asked R to read the Stata file by entering
>>
>> pol572a1<- read.dta("C:\\alex\\Graduate Coursework\\Pol
>> 572\\pol572a1.dta") 
> 
> At this point you should type str(pol572a1) to make sure <everything> 
> is the dataframe named pol572a1.
> 
>> So now I can do a few things with the data, but I am only able to do
>> so by entering
>>
>> with(pol572a1,
>>
>> before typing another command. So I enter the following for a
>> scatter plot: with(pol572a1, plot(rgnpc, incmean))
> 
> If you wanted to avoid the with() function (but why would you?) you 
> could have used:
>  
> plot(pol572a1$rgnpc, pol572a1$incmean)
> 
>> When I run a simple linear regression, I enter the following:
>> with(pol572a1, lm(incmean~rgnpc))
> 
> Which creates the model and immediately discards it, because no durable 
> object was given the values:
>  
>> But when try to get a fitted line, I enter the following:
>> with(pol572a1, lm( share.gnp)<-lm(incmean~rgnpc))  
> 
> That does not look particular sensible. Assuming that the goal was to 
> create a model object named share.gnp, then try instead:
> 
> with(pol572a1, share.gnp.mdl <-lm(incmean~rgnpc) ) 

That won't work:  share.gnp.mdl will be created in the local environment 
created by with(), and then discarded.  You need to put it outside, i.e.

share.gnp.mdl <- with(pol572a1, lm(incmean~rgnpc) )

Duncan Murdoch

> 
> (My practice is to label my models, but it is not necessary.)
> 
> Then look at share.gnp.mdl with str() and you should see fitted.values. 
> You could then plot() the fitted values and the observed values.
> 
> 
>> But I get the
>> following error message: Error in lm(share.gnp) <- lm(incmean ~
>> rgnpc) : object "share.gnp" not found 
>>
>> So what should I do to get R to read the dataframe in the ordinary
>> way with the usual command?  
> 
> I cannot tell what you mean. It appears you already have the data in a 
> dataframe.
> 
>> I am willing to scrap this dataframe
>> and use the original Stata file to start over, as long as that
>> resolves the problem. 
>>
>> Thanks!
>>
>> Alex
>>
> 
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