[R] See the numeric codes of a factor

[Bert Gunter]

Talk to a local statistician or study a book on regression. You do not
understand how regression works.

In R, see ?contrasts  .

-- Bert

Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374

"Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom."
Clifford Stoll




On Fri, Sep 19, 2014 at 5:55 AM, Angel Rodriguez
<angel.rodriguez at matiainstituto.net> wrote:
> Well, a variable with values 0/1 is useful for calculating observed probabilities by groups. But it is not diffcult to have the same variable both as numeric and as a factor in the dataframe and use each variation depending on the analysis.
>
> Angel
>
> ________________________________
>
> De: Duncan Murdoch [mailto:murdoch.duncan at gmail.com]
> Enviado el: vie 19/09/2014 14:22
> Para: Angel Rodriguez; r-help at r-project.org
> Asunto: Re: [R] See the numeric codes of a factor
>
>
>
> On 19/09/2014 8:12 AM, Angel Rodriguez wrote:
>> Re: [R] See the numeric codes of a factor
>> Thank you, Duncan. So isn't it possible to add labels to a variable
>> with numeric values 0/1? This kind of variable is very useful for
>> logistic regression, for example, but I'd rather have its
>> categories labelled.
>
> I think you are thinking of how you have done things in some other
> system.  In R, a factor is fine in logistic regression, regardless of
> the fact that internally values are stored as 1 and 2.
>
> Duncan Murdoch
>
>> Angel
>>
>> ------------------------------------------------------------------------
>> *De:* Duncan Murdoch [mailto:murdoch.duncan at gmail.com]
>> *Enviado el:* vie 19/09/2014 13:32
>> *Para:* Angel Rodriguez; r-help at r-project.org
>> *Asunto:* Re: [R] See the numeric codes of a factor
>>
>> On 19/09/2014, 6:53 AM, Angel Rodriguez wrote:
>> > Dear Subscribers,
>> >
>> > I want to label a numeric variable 0="Bad" /1="Good". I understand
>> the only way is to transform it into a factor variable.
>> >
>> > Is there a way to check that the numeric values of the new factor
>> variable are 0 and 1 and not 1 and 2?
>>
>> If you apply as.numeric() to a factor, you won't get a zero value.
>> Internal factor values start at 1.
>>
>> So I wouldn't rely on the internal storage to achieve whatever it is you
>> want to achieve.  Use explicit computation, e.g.
>>
>> words <- ifelse(var == 0, "Bad", ifelse(var == 1, "Good", NA))
>> values <- ifelse(words == "Bad", 0, ifelse(words == "Good", 1, NA))
>>
>> Duncan Murdoch
>>
>>
>>
>
>
>
>
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