R help - Jun 2011 - 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
as.numeric(df.$x) is not correct
class(df.$x)

Hi
> 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"?

from help page
?apply
Arguments
X
an array, including a matrix.

array is not a data frame
> apply(df, 2, class)
> class(df$x)
> class(df$group)
> class(df$y)
sapply(df, class)
        x     group         y 
"integer"  "factor" "numeric" 

> 
> 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.$x)) # seems bulky; note that 
> as.numeric(df.$x) is not correct
Actually it is correct in a sense it behaves as documented

?factor

Warning
The interpretation of a factor depends on both the codes and the
"levels"
attribute. Be careful only to compare factors with the same set of levels 
(in the same order). In particular, as.numeric applied to a factor is 
meaningless, and may happen by implicit coercion. To transform a factor f 
to approximately its original numeric values, as.numeric(levels(f))[f] is 
recommended and slightly more efficient than as.numeric(as.character(f)). 


Regards
Petr
> class(df.$x)



> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

> 
> 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)
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Dear Petr,

thanks for your posts, they perfectly answered my questions.

Cheers,

Marius


On 2011-06-28, at 09:49 , Petr PIKAL wrote:
>> 
>> 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)
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>