[R] Help on indicator variables

peter dalgaard
Fri, 22 Mar 2013 08:48:32 -0000

What Bill says, plus the fact that the default handling of logicals in modelling
is to convert them to factors and then use treatment contrasts, which will
effectively give you the right indicator variables automagically (This in
contrast to SAS where you can confuse yourself by declaring a 0/1 variable as a
CLASS variable):

> cond <- rep(c(TRUE, FALSE),4)
> y <- rnorm(8)
> lm(y~cond)

Call:
lm(formula = y ~ cond)

Coefficients:
(Intercept)     condTRUE
    -0.5741       1.1845

> lm(y~as.numeric(cond))

Call:
lm(formula = y ~ as.numeric(cond))

Coefficients:
     (Intercept)  as.numeric(cond)
         -0.5741            1.1845


On Mar 21, 2013, at 15:49 , William Dunlap wrote:

> I would use a logical variable, with values TRUE and FALSE, instead
> of a numeric indicator.  E.g., I find the following easier to follow
>    bL <- ABS==1 | DEFF==1
>    if (any(bL)) { do.this() }
> than
>    bN <- ifelse(ABS == 1 | DEFF == 1, 1, 0)
>    if (any(bN == 1)) { do.this() }
> The latter leaves me wondering what other values bN might have;
> the former makes it clear this is a TRUE/FALSE dichotomy.
>
> Logicals get converted to numbers (FALSE->0, TRUE->1) when used in
> arithmetic so you can do, e.g., mean(bL) to see what proportion of
> your cases satisfy the condition.
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org] On Behalf
>> Of Tasnuva Tabassum
>> Sent: Thursday, March 21, 2013 6:03 AM
>> To: R help
>> Subject: [R] Help on indicator variables
>>
>> I have two indicator variables ABS and DEFF. I want to create another
>> indicator variable which will take value 1 if either ABS=1 or DEFF=1.
>> Otherwise, it will take value 0. How can I make that?
>>
>> 	[[alternative HTML version deleted]]
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.

--
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com