[R] Applyiing mode() or class() to each column of a data.frame XXXX

[Hadley Wickham]

But be careful because class is a character vector (not necessarily a
character vector of length 1)

On Fri, Dec 30, 2011 at 10:21 AM, Justin Haynes <jtor14 at gmail.com> wrote:
> there is also colwise in the plyr package.
>
>> library(plyr)
>> colwise(class)(data6)
>      v13     v14       v15     f4     v16
> 1 integer numeric character factor logical
>
>
> Justin
>
>
> On Thu, Dec 29, 2011 at 4:47 PM, Jean V Adams <jvadams at usgs.gov> wrote:
>
>> Dan Abner wrote on 12/29/2011 06:13:11 PM:
>>
>> > Hi everyone,
>> >
>> > I am attempting to use the apply() function to obtain the mode and class
>> of
>> > each column in a data frame, however, I am encountering unexpected
>> results.
>> > I have the following example data:
>> >
>> >
>> > v13<-1:6
>> > v14<-c(1,2,3,3,NA,1)
>> > v15<-c("Good","Bad",NA,"Good","Bad","Bad")
>> > f4<-factor(rep(c("Blue","Red","Green"),2))
>> > v16<-c(F,T,F,F,T,F)
>> > data6<-data.frame(v13,v14,v15,f4,v16)
>> > data6
>> >
>> >
>> > Here is my function definition:
>> >
>> >
>> > contents<-function(x){
>> >  output<-data.frame(Varnum=1:ncol(x),
>> >   Name=names(x),
>> >   Mode=apply(x,2,mode),
>> >   Class=apply(x,2,class))
>> >  print(output)
>> > }
>>
>>
>> Use sapply() instead of apply().  In the help file for apply() it says: "
>> If X is not an array but an object of a class with a non-null dim value
>> (such as a data frame), apply attempts to coerce it to an array via
>> as.matrix if it is two-dimensional (e.g., a data frame) or via as.array."
>> This coercion to a matrix might be causing the unexpected result. sapply()
>> and lapply() are designed specifically for lists (which a data frame is).
>> I also simplified the function a bit ...
>>
>> contents<-function(x){
>>        data.frame(Varnum=1:ncol(x), Name=names(x),
>>        Mode=sapply(x,mode), Class=sapply(x,class))
>>        }
>>
>> Jean
>>
>>
>> > ====
>> >
>> > When I call the function, I obtain the following:
>> >
>> >
>> > > contents(data6)
>> >     Varnum Name      Mode     Class
>> > v13      1  v13 character character
>> > v14      2  v14 character character
>> > v15      3  v15 character character
>> >   f4       4   f4 character character
>> > v16      5  v16 character character
>> >
>> > =====
>> >
>> > Any help is appreciated.
>> >
>> > Thank you,
>> >
>> > Dan
>> >
>> >    [[alternative HTML version deleted]]
>> >
>> > ______________________________________________
>> > 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.
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> 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.
>>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.



-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/