[R] Creating Dummy Var in R for regression?

[Shivi Bhatia]

Thanks you all for the assistance. This really helps.

Hi Bert: While searching nabble i got to know R with factors variables
there is no need to create dummy variable. However please consider this
situation:
I am in the process of building a logistic regression model on NPS data.
The outcome variable is CE i.e. customer experience which has 3 rating so
ordinal logistic regression will be used. However most of my variables are
categorical. For instance one of the variable is agent knowledge which is a
10 point scale.

This agent knowledge is again a 3 rated scale: high medium low hence i need
to group these 10 values into 3 groups & then as you suggested i can
directly enter them in the model without creating n-1 categories.

I have worked on SAS extensively hence found this a bit confusing.

Thanks for the help.

On Sat, Aug 6, 2016 at 2:30 AM, Bert Gunter <bgunter.4567 at gmail.com> wrote:

> Just commenting on the email subject, not the content (which you have
> already been helped with): there is no need to *ever* create a dummy
> variable for regression in R if what you mean by this is what is
> conventionally meant. R will create the model matrix with appropriate
> "dummy variables" for factors as needed. See ?contrasts and ?C for
> relevant details and/or consult an appropriate R tutorial.
>
> Of course, if this is not what you meant, than ignore.
>
> Cheers,
> Bert
>
>
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>
>
> On Fri, Aug 5, 2016 at 1:49 PM,  <ruipbarradas at sapo.pt> wrote:
> > Hello,
> >
> > Your ifelse will never work because
> > reasons$salutation== "Mr" & reasons$salutation=="Father" is always FALSE
> > and so is reasons$salutation=="Mrs" & reasons$salutation=="Miss".
> > Try instead | (or), not & (and).
> >
> > Hope this helps,
> >
> > Rui Barradas
> >
> >
> >
> > Citando Shivi Bhatia <shivipmp82 at gmail.com>:
> >
> >> Dear Team,
> >>
> >> I need help with the below code in R:
> >>
> >> gender_rec<- c('Dr','Father','Mr'=1, 'Miss','MS','Mrs'=2, 3)
> >>
> >> reasons$salutation<- gender_rec[reasons$salutation].
> >>
> >> This code gives me the correct output but it overwrites the
> >> reason$salutation variable. I need to create a new variable gender to
> >> capture gender details and leave salutation as it is.
> >>
> >> i tried the below syntax but it is converting all to 1.
> >>
> >> reasons$gender<- ifelse(reasons$salutation== "Mr" & reasons$salutation==
> >> "Father","Male", ifelse(reasons$salutation=="Mrs" &
> reasons$salutation==
> >> "Miss","Female",1))
> >>
> >> Please suggest.
> >>
> >>         [[alternative HTML version deleted]]
> >>
> >> ______________________________________________
> >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.htmland provide commented,
> >> minimal, self-contained, reproducible code.
> >
> >
> >
> >         [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/
> posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
>

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