[R] Assignment converts variable to factor

[David Kane <David Kane]

Daniel Mastropietro writes:
 > Hello,
 > 
 > I would like to know if this behaviour in R is as expected.

It is as expected in R 1.5.1. Note that the NEWS for R-devel (1.6.0 to be)
says:


    o	[[<-.data.frame no longer coerces character replacement values
	to factor.  This is consistent with using $ to replace and
	with S4.

So, as best that I understand the details, the behavior will be changing. There
was some discussion of this topic on r-help and r-devel a month or two ago
(consisting mostly of my confusion and Brian Ripley's patient explanations). 

See:

http://www.r-project.org/nocvs/mail/r-help/2002/4016.html

Or the thread beginning with:

http://www.r-project.org/nocvs/mail/r-devel/2002/0777.html

Regards,

Dave Kane

 > I have a data frame 'dat' with column var1 being character (and not 
 > factor). Then I create a new column 'var2' by:
 > 
 >  > dat[,"var2"] <- dat$var1;
 > 
 > Column var2 is now a factor.
 > 
 > But if I do:
 > 
 >  > dat$var2 <- dat$var1;
 > 
 > Then column var2 is character (and not factor).
 > 
 > I don't want to have var2 as factor by doing the first assignment. I tried 
 > using 'as.character(dat$var1)' or converting dat[,"var2"] to character by 
 > using as.character() after the assignment, but still var2 is treated as factor.
 > 
 > Note that I want to use dat[,"var2"] and not dat$var2 because I am doing 
 > the assignment within a function by referencing column var2 with a variable 
 > whose value is "var2" (e.g. dat[,col2] <- dat$var1, where col2 = "var2"). 
 > It is easier and more clear to use the [] operator to reference a data 
 > frame column with a variable, rather than using the $ operator with the 
 > parse() function.
 > 
 > Thanks
 > Daniel Mastropietro
 > 	
 > 
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-- 
David Kane
Geode Capital Management
617-563-0122
david.d.kane at fmr.com
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