[R] Column sums from a data frame (without the headers)

[Gavin Simpson]

On Fri, 2008-02-29 at 12:02 -0500, Jason Horn wrote:
> Does anyone know how to get a vector of column sum from a data frame?   
> You can use colSums(), but this gives you a object of type "numeric"  
> with the column labels in the first row, and the sums in the second  
> row.  I just want a vector of the sums, and I can't figure out a way  
> to index the "numeric" object.
> 
> Thanks!

The labels you are seeing are just the 'names' attribute of the vector
of column sums that is being printed. You can ignore them for most uses
such as using them in some computations:

> df <- data.frame(A = runif(10), B = runif(10), C = rnorm(10))
> colSums(df)
        A         B         C 
 5.982975  5.566133 -4.696136 
> str(colSums(df))
 Named num [1:3]  5.98  5.57 -4.70
 - attr(*, "names")= chr [1:3] "A" "B" "C"
> colSums(df) * 4
        A         B         C 
 23.93190  22.26453 -18.78454

If you really need to get rid of the names:

> unname(colSums(df))
[1]  5.982975  5.566133 -4.696136

HTH

G

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