On Jul 12, 2010, at 11:19 AM, Duncan Murdoch wrote:
On 12/07/2010 11:10 AM, g...@ucalgary.ca wrote:
I would like to sum/mean/min a list of lists and numbers to return
the
related lists.
-1+2*c(1,1,0)+2+c(-1,10,-1) returns c(2,13,0) but
sum(1,2*c(1,1,0),2,c(-1,10,-1)) returns 15 not a list.
Using the suggestions of Gabor Grothendieck,
Reduce('+',list(-1,2*c(1,1,0),2,c(-1,10,-1))) returns what we want,
c(2,13,0).
However, it seems that this way does not work to mean/min.
So, how to mean/min a list of lists and numbers to return a list?
Thanks,
You need to be careful of terminology: c(1,1,0) is not a list, it's
a vector. What you want is to apply functions componentwise to
lists of vectors.
One way to do that is to bind them into a matrix, and use apply.
For example:
M <- cbind(-1, c(1,1,0), c(-1,10,-1))
apply(M, 1, mean)
As usual Duncan's understanding is better than mine. Just so you know,
there are also utility functions row-oriented functions which are
conisderably faster when they are the correct solution:
?rowSums
?rowMeans
> rowMeans(cbind(-1, c(1,1,0), c(-1,10,-1)) )
[1] -0.3333333 3.3333333 -0.6666667
> apply(cbind(-1, c(1,1,0), c(-1,10,-1)), 1, mean)
[1] -0.3333333 3.3333333 -0.6666667
... and there is a parallel" version of a minimum functions, pmin
that would have given you results for arguments that are just the
vectors of varying length you were working with:
> pmin(2, c(2,2,0) ,-1 , c(-1,10,-1))
#[1] -1 -1 -1 #(Done with argument recycling.)
Duncan Murdoch
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