[R] Creating Dummy Var in R for regression?

jeremiah rounds roundsjeremiah at gmail.com
Sat Aug 6 01:31:12 CEST 2016


Something like:

d  =  data.frame(score = sample(1:10, 100, replace=TRUE))
d$score_t = "low"
d$score_t[d$score > 3] = "medium"
d$score_t[d$score >7 ] = "high"
d$score_t = factor(d$score_t, levels = c("low", "medium", "high"),
ordered=TRUE)  #set ordered = FALSE for dummy variables
X = model.matrix(~score_t, data=d)
X



On Fri, Aug 5, 2016 at 3:23 PM, Shivi Bhatia <shivipmp82 at gmail.com> wrote:

> 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.
> >
>
>         [[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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