[R] Creating Dummy Var in R for regression?

[Fredrik Karlsson]

Hi,

please also have a look at the 'cut' function.Very handa function for these
types of situations.

Best,

Fredrik

On Sun, Aug 7, 2016 at 8:10 PM, Shivi Bhatia <shivipmp82 at gmail.com> wrote:

> Thank you Jeremiah and all others for the assistance. This really helped.
>
> On Sat, Aug 6, 2016 at 5:01 AM, jeremiah rounds <roundsjeremiah at gmail.com>
> wrote:
>
> > 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/posti
> >> ng-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.
>



-- 
"Life is like a trumpet - if you don't put anything into it, you don't get
anything out of it."

	[[alternative HTML version deleted]]