Odp: data.frame: How to get the classes of all components and how to remove their factor structure?

Dear expeRts,

I have two questions concerning data frames:
(1) How can I apply the class function to each component in a 
data.frame?
As you can see below, applying class to each column is not the right 
approach; applying it to each component seems bulky.
(2) After transforming the data frame a bit, the classes of certain 
components change to factor. How can I remove the factor structure?

Cheers,

Marius

x <- c(2004:2010, 2002:2011, 2000:2011)
df <- data.frame(x=x, group=c(rep("low",7), rep("middle",10), 
rep("high",12)),
                 y=x+100*runif(length(x))) 

## Question (1): why do the following lines do not give the same 
"class"?
apply(df, 2, class)
class(df$x)
class(df$group)
class(df$y)

df. <- as.data.frame(xtabs(y ~ x + group, data=df))

class(df.$x)
class(df.$group)
class(df.$Freq)

## Question (2): how can I remove the factor structure from x?
df.$x <- as.numeric(as.character(df.$x)) # seems bulky; note that 
If you do it often you can

unfactor <- function(x) as.numeric(as.character(x))
df.$x <- unfactor(df.$x)

or you can use 
df. <- as.data.frame(xtabs(y ~ x + group, data=df), 
stringsAsFactors=FALSE)
df.$x <- as.numeric(df.$x)

But it seems to me that it is not much less bulkier.

Regards
Petr
as.numeric(df.$x) is not correct
class(df.$x)
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Odp: data.frame: How to get the classes of all components and how to remove their factor structure?

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