[R] class in apply

[Stéphane Dray]

apply transorm your data.frame into a matrix which can contains only one 
type of values (character or numeric or logical).
data.frame are list, so they can contain various kind of data, and a 
solution to your problem is given by lapply:

 > b=lapply(df, function(r) print(class(r['a'])))
[1] "numeric"
[1] "factor"

>Numeric data that is part of a mixed type data frame is converted into
>character. How can I tell apply to maintain the original class of a
>column and not convert it into character. I would like to do this of
>the vector and not inside the apply function individually over each
>element. Consider the following two scenarios, in the second column
>'a' maintained its class while it lost its numeric type in the first
>case.
>
>  
>
>>df = data.frame(a=c(1,2), b=c('A','B'))
>>df
>>    
>>
>  a b
>1 1 A
>2 2 B
>  
>
>>a=apply(df, 1, function(r) print(class(r['a'])))
>>    
>>
>[1] "character"
>[1] "character"
>  
>
>>a=apply(df, 1, function(r) print(class(r['b'])))
>>    
>>
>[1] "character"
>[1] "character"
>
>
>  
>
>>df = data.frame(a=c(1,2))
>>df
>>    
>>
>  a
>1 1
>2 2
>  
>
>>a=apply(df, 1, function(r) print(class(r['a'])))
>>    
>>
>[1] "numeric"
>[1] "numeric"
>
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-- 
StÃ©phane DRAY (dray at biomserv.univ-lyon1.fr )
Laboratoire BBE-CNRS-UMR-5558, Univ. C. Bernard - Lyon I
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