[R] Creating Dummy Var in R for regression?

[Shivi Bhatia]

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.
>>
>
>

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