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

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

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