R help - Aug 2010 - strange behavior of ifelse with factors

Dear R experts:  this is probably correct behavior, but I do want to
point out that it is unexpected to someone not too well versed:
> test=factor("A","B","C","A")
> ifelse(test=="A", as.factor("A"), test)
[1] 1 2 3 1

ok, my factor was just coerced into integers, even though I have a
logical vector as my condition and factors as my true and false
values.  this means that
> test[1:3]=ifelse(test[1:3]=="A", rep(as.factor("A"),3),
test[1:3])
won't work.  I do know how to program around this, but since it
stumped me for a while (in a more complex program, of course), I
thought I would drop this note.

regards,

/iaw
----
Ivo Welch (ivo.welch at brown.edu, ivo.welch at gmail.com)

This is mentioned on page 70 of 'The R Inferno'.

On 20/08/2010 22:38, ivo welch wrote:
> Dear R experts:  this is probably correct behavior, but I do want to
> point out that it is unexpected to someone not too well versed:
>
>> test=factor("A","B","C","A")
>> ifelse(test=="A", as.factor("A"), test)
> [1] 1 2 3 1
>
> ok, my factor was just coerced into integers, even though I have a
> logical vector as my condition and factors as my true and false
> values.  this means that
>
>> test[1:3]=ifelse(test[1:3]=="A",
rep(as.factor("A"),3), test[1:3])
>
> won't work.  I do know how to program around this, but since it
> stumped me for a while (in a more complex program, of course), I
> thought I would drop this note.
>
> regards,
>
> /iaw
> ----
> Ivo Welch (ivo.welch at brown.edu, ivo.welch at gmail.com)
>
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-- 
Patrick Burns
pburns at pburns.seanet.com
http://www.burns-stat.com
(home of 'Some hints for the R beginner'
and 'The R Inferno')