I tried the following:
m <- matrix(runif(100000),1000,100)
junk <- gc()
print(system.time(for(i in 1:100) X1 <- do.call(pmax,data.frame(m))))
junk <- gc()
print(system.time(for(i in 1:100) X2 <- apply(m,1,max)))
and got
user system elapsed
2.704 0.110 2.819
user system elapsed
1.938 0.098 2.040
so unless there's something that I am misunderstanding (always a serious
consideration) Wacek's apply method looks to be about 1.4 times
*faster* than
the do.call/pmax method.
cheers,
Rolf Turner
On 30/03/2009, at 3:55 PM, Bert Gunter wrote:
If speed is a consideration,availing yourself of the built-in pmax()
function via
do.call(pmax,data.frame(yourMatrix))
will be considerably faster for large matrices.
If you are puzzled by why this works, it is a useful exercise in R
to figure
it out.
Hint:The man page for ?data.frame says:
"A data frame is a list of variables of the same length with unique
row
names, given class 'data.frame'."
Cheers,
Bert
Bert Gunter
Genentech Nonclinical Statistics
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
project.org] On
Behalf Of Wacek Kusnierczyk
Sent: Saturday, March 28, 2009 5:22 PM
To: Ana M Aparicio Carrasco
Cc: r-help@r-project.org
Subject: Re: [R] Matrix max by row
Ana M Aparicio Carrasco wrote:
I need help about how to obtain the max by row in a matrix.
For example if I have the following matrix:
2 5 3
8 7 2
1 8 4
The max by row will be:
5
8
8
matrix(apply(m, 1, max), nrow(m))
vQ
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