As others noted, you can use the built in function colSums, but you
said you're writing your own. Given what you've got so far, that
makes the issue one of structuring the output.
Try
csum <- function(m)
{
a = data.frame(m)
s = lapply(a,sum)
unlist(s)
}
lapply() returns a list, so you have to use unlist() on it in order
to restructure the list into a vector.
However:
Converting the matrix to a dataframe is not needed; you can use the
apply() function on the matrix, as suggested by Jorge, in which case
the result will already be a vector, so you won't need to unlist().
Then it's much simpler:
csum <- function(m) apply(m,2,sum)
A couple of other notes:
Using return() is unnecessary in such a simple function.
Be careful with terminology. You said you want the result as a single
"list". But a list, in R, is an object with a particular structure,
but *not* the structure you appear to be looking for, since your
description "[1] 6 15 24" looks like a vector, not a list.
-Don
At 11:25 AM -0700 7/16/09, voidobscura wrote:
Alright, so I am trying to write my own function to calculate column sums in
a matrix. I want the result as a single list with the values.
So far I have:
csum<-function(m)
{
a = data.frame(m)
s = lapply(a,sum)
return(s)
}
What is the easiest way to have it return in a format such as [1] 6 15 24 ?
Thanks.
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--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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