[R] Recoding lists of categories of a variable

Fox, John jfox at mcmaster.ca
Mon Oct 10 21:31:43 CEST 2016

Dear Margaret,

You've had one suggestion of an alternative for recoding variables, but in addition your code is in error (see below).

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
> Sent: Monday, October 10, 2016 10:56 AM
> To: r-help at r-project.org
> Subject: [R] Recoding lists of categories of a variable
> Hello
> The R code
> mydata$newvar[oldvar = "topic1"] <- "parenttopic"

That should be

   mydata$newvar[oldvar == "topic1"] <- "parenttopic"

Moreover, the code assumes that oldvar is visible, which may not be the case if it lives in mydata and mydata isn't attach()ed.


John Fox, Professor
McMaster University
Hamilton, Ontario, Canada
Web: socserv.mcmaster.ca/jfox

> is intended to recode the category 'topic 1' of the old  varaible
> 'oldvar' a new category label 'parenttopic' by defining the new variable
> 'newvar'.
> Is there a convenient way to edit this code to allow me to recode a list
> of categories 'topic 1', 'topic 9' and 'topic 14', say, of the the old
> variable 'oldvar' as 'parenttopic' by means of the new variable
> 'newvar', while also mapping system missing values to system missing
> values?
> Thanks in advance
> Best wishes
> Margaret

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