[R] Excluding data with apply

[David Winsemius]

Using indexing and putting a minus sign in front of a vector of column  
names that you want to exclude would be a typical approach:

df <- data.frame(a=LETTERS[1:4], b= rnorm(4), c=rnorm(4), d=  
letters[5:9])

apply(df[ , -c("a","d")], 2, sum)

(Pretty sure this will run properly but don't have R up an runnign to  
test it.)



-- 
David Winsemius

On Jan 8, 2009, at 5:52 AM, Christian Kamenik wrote:

> Dear all,
>
> 'Apply' is a great thing for running functions on rows or columns of  
> a matrix:
>
> X <- rnorm(20, mean = 0, sd = 1)
> dim(X) <- c(5,4)
> apply(X,2,sum)
>
> Is there a way to use apply for excluding rows or columns from a  
> matrix to run functions on the remaining rows or columns? I know, I  
> could do this with a 'for' loop, but 'apply' would be much easier  
> and quicker, and require less programming...
>
> Cheers, Christian
>
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