[R] bug in 'margins' behavior in reshape - cast

[mfrumin]

according to the documentation of the cast function in the reshape function,
I would expect this bit of code from the examples to calculate marginal
means over only the 'diet' variable.  

#Chick weight example
names(ChickWeight) <- tolower(names(ChickWeight))
chick_m <- melt(ChickWeight, id=2:4, na.rm=TRUE)
cast(chick_m, diet + chick ~ time, mean, margins="diet")

But, 
summary(cast(subset(chick_m, time == 0), diet + chick ~ time, mean,
margins="diet")) returns:

    diet        chick          0        
 1    :21   (all)  : 4   Min.   :39.00  
 2    :11   18     : 1   1st Qu.:40.85  
 3    :11   16     : 1   Median :41.00  
 4    :11   15     : 1   Mean   :41.05  
 (all): 0   13     : 1   3rd Qu.:42.00  
            9      : 1   Max.   :43.00  
            (Other):45                  

which shows that it calculated margins on the 'chick' column as well.  this
behavior causes great problems for me when in my data one of the columns is
a non-factor column, eg a Date, but the unrequested margining behavior turns
that column into a factor.

am I missing something?

Thanks,
Mike
-- 
View this message in context: http://www.nabble.com/bug-in-%27margins%27-behavior-in-reshape---cast-tp18737649p18737649.html
Sent from the R help mailing list archive at Nabble.com.