R help - Feb 2008 - Column sums from a data frame (without the headers)

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!

colSums gives you exactly what you want, but the vector is *named*.
You can use it like a not-named numeric vector, without much trouble.
If you still want to get rid of the names see ?unname

G.

On Fri, Feb 29, 2008 at 12:02:46PM -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!
> 
> ______________________________________________
> 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.
-- 
Csardi Gabor <csardi at rmki.kfki.hu>    UNIL DGM

Jason -

colSums does return an object of class "numeric", which is certainly a
vector.  The vector it returns happens to have names.  If you want an 
unnamed vector of the sums, just set the names attribute to NULL. This 
will remove the names.  However, you say you can't figure out how to 
index the object that colSums returns.  You index it just like any other 
vector, but you can use names in addition.

## ALL UNTESTED!
## test data.frame
testdf <- data.frame(a = rnorm(10), b = rnorm(10))
cs <- colSums(testdf)

class(cs)  ## numeric
is.vector(cs)  ## TRUE
names(cs) ## look at the names of the vector

cs[1] ## first element of cs
cs["a"] ## same as above

## get rid of names attribute
names(cs) <- NULL
cs  ## look at cs, no more names
cs[1] ## still works
cs["a"] ## no longer works

Best,
Erik Iverson

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!
> 
> ______________________________________________
> 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.

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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as.vector(col.Sums())

Ben 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Jason Horn
Sent: Friday, February 29, 2008 11:03 AM
To: R-help at stat.math.ethz.ch
Subject: [PS] [R] Column sums from a data frame (without the headers)

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!

______________________________________________
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.