[R] lapply drops colnames

Gabor Grothendieck ggrothendieck at myway.com
Tue Aug 3 02:48:02 CEST 2004

Jack Tanner <ihok <at> hotmail.com> writes:

> Wolski wrote:
> > What you can do is to extend the column (list) by an addtional attribute 
> attr(mydataframe[i],"info")<-names(mydataframe)[i] and store theyr names in 
> OK, that's brilliant. Any ideas on how to do this automatically for 
> every column in my dataframe? lapply(dataframe... fails for the obvious 
> reason. Should I do something like this, or is for() to be avoided even 
> in this case?
>  > for(i in 1:length(a)) {print(names(a)[i])}

You can also lapply or sapply over indices or even the column names
themselves like this:


# sapplying over indices

res <- sapply(1:ncol(iris), function(i) {
       cat("1st element of", colnames(iris)[i], "is", iris[1,i], "\n")
} )

# sapplying over column names

res <- sapply(colnames(iris), function(s) {
       cat("1st element of", s, "is", iris[1,s], "\n")
} )

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