R help - Oct 2012 - warning in summary(aov())

Hi R-listers,

I am receiving an error - see below. Aeventexhumed is the event in which
nesting occured, so it is defined by A, B, C. I thought as a factor was ok,
tried to change it to as.character but it still gave me the same error. Is
there something I should do about this error or just ignore it? 

Please advise, Jean
>summary(aov(EDI ~ HTLIndex + Aeventexhumed + HTLIndex:Aeventexhumed,
data=data.to.analyze))

                       Df  Sum Sq Mean Sq F value Pr(>F)
HTLIndex                6   2.435 0.40575  0.2027 0.9752
Aeventexhumed           2   4.652 2.32601  1.1619 0.3172
HTLIndex:Aeventexhumed 11   7.941 0.72192  0.3606 0.9680
Residuals              98 196.193 2.00197               
5 observations deleted due to missingness
Warning message:
In model.matrix.default(mt, mf, contrasts) :
  variable 'Aeventexhumed' converted to a factor



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On Sat, Oct 6, 2012 at 9:12 AM, Jhope <jeanwaijang at gmail.com>
wrote:
> Hi R-listers,
>
> I am receiving an error - see below. Aeventexhumed is the event in which
> nesting occured, so it is defined by A, B, C. I thought as a factor was ok,
> tried to change it to as.character but it still gave me the same error. Is
> there something I should do about this error or just ignore it?
>
> Please advise, Jean
>
>>summary(aov(EDI ~ HTLIndex + Aeventexhumed + HTLIndex:Aeventexhumed,
> data=data.to.analyze))
>
>                        Df  Sum Sq Mean Sq F value Pr(>F)
> HTLIndex                6   2.435 0.40575  0.2027 0.9752
> Aeventexhumed           2   4.652 2.32601  1.1619 0.3172
> HTLIndex:Aeventexhumed 11   7.941 0.72192  0.3606 0.9680
> Residuals              98 196.193 2.00197
> 5 observations deleted due to missingness
> Warning message:
> In model.matrix.default(mt, mf, contrasts) :
>   variable 'Aeventexhumed' converted to a factor
I think you should have only seen this when Aeventexhumed was a
character -- it's nothing to worry about, just letting you know a
factor conversion had to happen (which is almost surely what you
wanted).

If you see this when Aeventexhumed is a factor already, that's
somewhat surprising. What does str(data.to.analyze) show you?

Michael
>
>
>
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Thank you Michael, 



Another new and useful function for me. In brief, str() gave me:

$ Aeventexhumed: chr  "A" "A" "A" "A"
...
$ Aeventexhumed: Factor w/ 4 levels
"","A","B","C": 2 2 2 2 2 2 2 2 2 2 ...

I think on the data sheet there are two columns for Aeventexhumed and only
one of them was converted to a factor. Factor is correct so as you suggested
I will just leave it. 

Thanks! Jean



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