[R] two apparent anomalies

[Berwin A Turlach]

On Sat, 22 Jan 2011 06:16:43 -0800 (PST)
"analyst41 at hotmail.com" <analyst41 at hotmail.com> wrote:

> (1)
> 
> > a = c("a","b")
> > mode(a)
> [1] "character"
> > b = c(1,2)
> > mode(b)
> [1] "numeric"
> > c = data.frame(a,b)
> > mode(c$a)
> [1] "numeric"

R> str(c)
'data.frame':	2 obs. of  2 variables:
 $ a: Factor w/ 2 levels "a","b": 1 2
 $ b: num  1 2

Character vectors are turned into factors by default by data.frame().

OTOH:

R> c = data.frame(a,b, stringsAsFactors=FALSE)
R> mode(c$a)  
[1] "character"

> (2)
> 
> 
> > a = c("a","a","b","b","c")
> > levels(as.factor(a))
> [1] "a" "b" "c"
> > levels(as.factor(a[1:3]))
> [1] "a" "b"
> > a = as.factor(a)
> > levels(a)
> [1] "a" "b" "c"
> > levels(a[1:3])
> [1] "a" "b" "c"

Subsetting factors does not get rid of no-longer used levels by default.

OTOH:

R> levels(a[1:3, drop=TRUE])
[1] "a" "b"

or

R> levels(factor(a[1:3]))
[1] "a" "b"


HTH.

Cheers,

	Berwin

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